Mapping Mountains – Significant Height Revisions – 100m Twmpau

 

100m Twmpau – Significant Height Revisions

The 100m Twmpau (an acronym for thirty welsh metre prominences and upward) are the Welsh hills at or above 100m and below 200m in height that have a minimum drop of 30m.  Accompanying the main P30 list is a sub list entitled the 100m Sub-Twmpau with the qualification to this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.

The list is authored by Myrddyn Phillips and the posts that have appeared on Mapping Mountains detailing the significant height revisions to the main P30 list and the sub list appear below presented chronologically in receding order.

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Coed Penllyn (SH 786 696) - 38th significant height revision

Summit Relocations post for Coed Penllyn

Significant Name Changes post for Coed Penllyn

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Coed Penllyn (SH 786 696)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Coed Penllyn, and this was derived from the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, and it is adjoined to the Mynydd Hiraethog group of hills, which are situated in the northern part of North Wales (Region A, Sub-Region A2), and it is positioned with the A470 road to its west and a minor road to its east, and has the town of Llanrwst towards the south.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 list, and listed with a 193m summit height positioned at SH 786 697 with an accompanying note stating; Height from 1989 1:50000 map. 

Extract from the Ordnance Survey 1:50,000 Landranger map

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed as a twin top with an estimated c 25m of drop, based on the 193m spot height that appears on the 1:50,000 Landranger map and a twin 193m map heighted top positioned at SH 78713 69823 that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and an estimated c 168m bwlch height, based on interpolation of 10m contouring between 160m – 170m. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Coed Penllyn (SH 786 696)

The summit height produced by LIDAR analysis is 198.0m and is positioned at SN 78630 69665, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 198.0m and this was derived from LIDAR analysis, this is 5.0m higher than the previously listed 193m summit height which appeared as a twin top with a spot height on the Ordnance Survey 1:50,000 Landranger map and the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

 

The full details for the hill are: 

Group:  Mynydd Hiraethog 

Name:  Coed Penllyn 

OS 1:50,000 map:  115

Summit Height (New Height):  198.0m (LIDAR) 

Summit Grid Reference:  SH 78630 69665 (LIDAR) 

Bwlch Height:  170.9m (LIDAR) 

Bwlch Grid Reference:  SH 78892 70134 (LIDAR) 

Drop:  27.1m (LIDAR) 

 

Myrddyn Phillips (March 2026)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Bryn Llwyn (SN 672 998) - 37th significant height revision

Hill Reclassifications post for Bryn Llwyn

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Bryn Llwyn (SN 672 998)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Bryn Llwyn, and it is adjoined to the Tarren y Gesail group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with a minor road to its north and the A493 road to its south-east, and has the village of Cwrt towards the east.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 list.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 27m of drop, based on an estimated c 173m summit height and an estimated c 146m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Bryn Llwyn (SN 672 998)

The summit height produced by LIDAR analysis is 175.4m and is positioned at SN 67202 99820, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 175.4m and this was derived from LIDAR analysis, this is 2.4m higher than the previously listed c 173m summit height which was estimated from interpolation of the uppermost 170m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are: 

Group:  Tarren y Gesail 

Name:  Bryn Llwyn 

OS 1:50,000 map:  135

Summit Height (New Height):  175.4m (LIDAR) 

Summit Grid Reference:  SN 67202 99820 (LIDAR) 

Bwlch Height:  145.4m (LIDAR) 

Bwlch Grid Reference:  SN 66942 99795 (LIDAR) 

Drop:  30.0m (LIDAR) 

 

Myrddyn Phillips (November 2025)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Crwn Hir (SN 670 993) - 36th significant height revision

Hill Reclassifications post for Crwn Hir

Significant Name Changes post for Crwn Hir

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Crwn Hir (SN 670 993)

The criteria for the list that this height revision applies to are: 

100m Twmpau - Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Crwn Hir, and this was derived from the Tithe map, and it is adjoined to the Tarren y Gesail group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with a minor road to its north and the A493 road to its east, and has the village of Cwrt towards the east north-east.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 20m of drop, based on an estimated c 146m summit height and an estimated c 126m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Crwn Hir (SN 670 993)

The summit height produced by LIDAR analysis is 151.4m and is positioned at SN 67079 99365, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 151.4m and this was derived from LIDAR analysis, this is 5.4m higher than the previously listed c 146m summit height which was estimated from interpolation of the uppermost 140m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are: 

Group:  Tarren y Gesail 

Name:  Crwn Hir 

OS 1:50,000 map:  135

Summit Height (New Height):  151.4m (LIDAR) 

Summit Grid Reference:  SN 67079 99365 (LIDAR) 

Bwlch Height:  121.25m (LIDAR) 

Bwlch Grid Reference:  SN 67030 99444 & SN 67034 99447 (LIDAR) 

Drop:  30.1m (LIDAR) 

 

Myrddyn Phillips (October 2025)

Mapping Mountains – Significant Height Revisions – 100m Twmpau

100m Twmpau – Significant Height Revisions

The 100m Twmpau (an acronym for thirty welsh metre prominences and upward) are the Welsh hills at or above 100m and below 200m in height that have a minimum drop of 30m.  Accompanying the main P30 list is a sub list entitled the 100m Sub-Twmpau with the qualification to this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.

The list is authored by Myrddyn Phillips and the posts that have appeared on Mapping Mountains detailing the significant height revisions to the main P30 list and the sub list appear below presented chronologically in receding order.

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Llety Llwydin (SN 672 923) - 35th significant height revision

Hill Reclassifications post for Llety Llwydin

Summit Relocations post for Llety Llwydin

Significant Name Changes post for Llety Llwydin

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Llety Llwydin (SN 672 923)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Llety Llwydin, and this was derived from the Tithe map, and it is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the north-western part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north, south and east, with the A487 road to its west, and has the town of Machynlleth towards the north-east.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 19m of drop, based on an estimated c 176m summit height and an estimated c 157m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Llety Llwydin (SN 672 923)

The summit height produced by LIDAR analysis is 178.8m and is positioned at SN 67233 92384, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 178.8m and this was derived from LIDAR analysis, this is 2.8m higher than the previously listed summit height which was estimated from interpolation of the uppermost 170m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Banc Llechwedd Mawr 

Name:  Llety Llwydin 

OS 1:50,000 map:  135

Summit Height (New Height):  178.8m (LIDAR) 

Summit Grid Reference:  SN 67233 92384 (LIDAR) 

Bwlch Height:  155.5m (LIDAR) 

Bwlch Grid Reference:  SN 66961 92762 (LIDAR) 

Drop:  23.3m (LIDAR) 

 

Myrddyn Phillips (August 2025) 

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Coed Cerrig Mawr (SN 688 944) - 34th significant height revision

Hill Reclassifications post for Coed Cerrig Mawr

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Coed Cerrig Mawr (SN 688 944)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Coed Cerrig Mawr, and it is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the north-western part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north and south-west, with the A487 road to its west, and has the town of Machynlleth towards the north-east.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 19m of drop, based on an estimated c 167m summit height and an estimated c 148m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Coed Cerrig Mawr (SN 688 944)

The summit height produced by LIDAR analysis is 171.8m and is positioned at SN 68824 94413, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 171.8m and this was derived from LIDAR analysis, this is 4.8m higher than the previously listed summit height which was estimated from interpolation of the uppermost 160m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Banc Llechwedd Mawr 

Name:  Coed Cerrig Mawr 

OS 1:50,000 map:  135

Summit Height (New Height):  171.8m (LIDAR) 

Summit Grid Reference:  SN 68824 94413 (LIDAR) 

Bwlch Height:  150.0m (LIDAR) 

Bwlch Grid Reference:  SN 68905 94399 (LIDAR) 

Drop:  21.8m (LIDAR) 

 

Myrddyn Phillips (July 2025)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Coed Cae Saer (SN 736 975) - 33rd significant height revision

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Coed Cae Saer (SN 736 975)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Coed Cae Saer, and it is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the north-western part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north-west, north-east and south, and the A487 road farther to its north-west, and has the town of Machynlleth towards the north north-east.

After the original 100m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website, were standardised and interpolated heights and drop values also included, this hill was listed with an estimated c 38m of drop, based on an estimated c 134m summit height and an estimated c 96m bwlch height, with both heights based on 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Coed Cae Saer (SN 736 975)

The summit height produced by LIDAR analysis is 139.9m and is positioned at SN 73665 97584, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 139.9m and this was derived from LIDAR analysis, this is 5.9m higher than the previously listed summit height which was estimated from interpolation of the uppermost 130m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Banc Llechwedd Mawr 

Name:  Coed Cae Saer 

OS 1:50,000 map:  135

Summit Height (New Height):  139.9m (LIDAR) 

Summit Grid Reference:  SN 73665 97584 (LIDAR) 

Bwlch Height:  93.8m (LIDAR) 

Bwlch Grid Reference:  SN 73495 97695 (LIDAR) 

Drop:  46.1m (LIDAR) 

 

Myrddyn Phillips (June 2025)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Cae Cefn (SO 315 009) - 32nd significant height revision

Hill Reclassifications post for Cae Cefn

Summit Relocations post for Cae Cefn

Significant Name Changes post for Cae Cefn

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Cae Cefn (SO 315 009)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cae Cefn and this was derived from the Tithe map, and it is adjoined to the Cefn yr Ystrad group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with minor roads to its west, south and east, and the A4042 road farther to its west, and has the town of Pont-y-pŵl (Pontypool) towards the west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

Extract from the Ordnance Survey 1:25,000 Explorer map

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with 19m of drop, based on the 156m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map and the 137m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

Extract from the Ordnance Survey 1:50,000 Landranger map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Cae Cefn (SO 315 009)

The summit height produced by LIDAR analysis is 159.4m and is positioned at SO 31564 00957 and SO 31565 00959, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 159.4m and this was derived from LIDAR analysis, this is 3.4m higher than the previously listed summit height which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger map.

 

The full details for the hill are:

Group:  Cefn yr Ystrad 

Name:  Cae Cefn 

OS 1:50,000 map:  171

Summit Height (New Height):  159.4m (LIDAR) 

Summit Grid Reference:  SO 31564 00957 & SO 31565 00959 (LIDAR) 

Bwlch Height:  135.7m (LIDAR) 

Bwlch Grid Reference:  SO 31507 01161 (LIDAR) 

Drop:  23.7m (LIDAR) 

 

Myrddyn Phillips (March 2025)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Comin Gwauncaegurwen (SN 738 129) - 31st significant height revision

Hill Reclassifications post for Comin Gwauncaegurwen

Significant Name Changes post for Comin Gwauncaegurwen

  

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Comin Gwauncaegurwen (SN 738 129)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Comin Gwauncaegurwen and this was derived from the Tithe map with the language protocol also instigated, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A4068 road to its north-east, the A4069 road to its west and a minor road to its south-east, and has the village of Brynaman towards the west north-west. 

Extract from the Ordnance Survey 1:50,000 Landranger map

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as with no significant contours of note on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map it was difficult to know whether any hill of note existed. 

Extract from the Ordnance Survey 1:25,000 Explorer map

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites. 

Extract from the interactive mapping hosted on the WalkLakes website

One of the mapping resources now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available maps and an uppermost 200m ring contour is given on the summit area of this hill.

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Comin Gwauncaegurwen (SN 738 129)

The height produced by LIDAR analysis to the summit of this hill is 196.6m positioned at SN 73812 12929, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height or uppermost ring contour has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 196.6m and this was derived from LIDAR analysis, this is 3.4m lower than the uppermost 200m ring contour that appears on the interactive mapping hosted on the WalkLakes website.

 

The full details for the hill are:

Group:  Mynydd Du 

Name:  Comin Gwauncaegurwen 

OS 1:50,000 map:  160

Summit Height (New Height):  196.6m (LIDAR) 

Summit Grid Reference:  SN 73812 12929 (LIDAR) 

Bwlch Height:  174.7m (LIDAR) 

Bwlch Grid Reference:  SN 73776 13436 (LIDAR) 

Drop:  21.8m (LIDAR) 

 

Myrddyn Phillips (October 2024)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Cefn (SH 721 004) - 30th significant height revision

Significant Name Changes post for Cefn

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Cefn (SH 721 004)

The criteria for the two lists that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

Y Trechol - The Dominant Hills of Wales - Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Cefn and this was derived from the Tithe map, and it is adjoined to the Tarren y Gesail group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with the A493 road to its north and the A487 road to its south, and has the town of Machynlleth towards the east.

After the original 100m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website were standardised and interpolated heights and drop values also included, this hill was listed with an estimated c 114m summit height, based on interpolation of its uppermost 110m ring contour, and the 59m bwlch spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, with these values giving this hill an estimated c 55m of drop and 48.25% dominance. 

Extract from the Ordnance Survey 1:25,000 Explorer map

The details for this hill were reassessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Intearctive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps, and for this hill it had a 119m summit spot height and when coupled with its 59m bwlch spot height, these values gave this hill 60m of drop and 50.42% dominance.

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Cefn (SH 721 004)

The height produced by LIDAR analysis to the summit of this hill is 118.2m positioned at SH 72126 00402, and this in relation to the original interpolated summit height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 118.2m and this was derived from LIDAR analysis, this is 4.2m higher than the original estimated summit height which was based on interpolation of the uppermsot 110m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Tarren y Gesail 

Name:  Cefn 

OS 1:50,000 map:  135

Summit Height (New Height):  118.2m (LIDAR) 

Summit Grid Reference:  SH 72126 00402 (LIDAR) 

Bwlch Height:  59.0m (LIDAR) 

Bwlch Grid Reference:  SH 72569 00795 (LIDAR) 

Drop:  59.2m (LIDAR) 

Dominance:  50.08% (LIDAR) 

 

Myrddyn Phillips (October 2024)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Pant y Brwynog (SN 548 037) - 29th significant height revision

Hill Reclassifications post for Pant y Brwynog

Summit Relocations post for Pant y Brwynog

Significant Name Changes post for Pant y Brwynog

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pant y Brwynog (SN 548 037)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Pant y Brwynog and this was derived from the Tithe map, and it is adjoined to the Mynydd Sylen group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with minor roads to its north-east, west and south, and the A476 road farther to its west, the A4138 road to its south-east and the M4 motorway farther to its east, and has the town of Pontarddulais towards the east.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 27m of drop, based on the 130m summit spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and an estimated c 103m bwlch height, based on interpolation of 5m contouring between 100m – 105m. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Pant y Brwynog (SN 548 037)

The height produced by LIDAR analysis to the natural summit of this hill is 127.65m positioned at SN 54886 03732, and this in relation to the spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 127.65m and this was derived from LIDAR analysis, this is 2.35m lower than the previously listed summit height which was based on the spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

The full details for the hill are:

Group:  Mynydd Sylen 

Name:  Pant y Brwynog 

OS 1:50,000 map:  159

Summit Height (New Height):  127.65m (LIDAR) 

Summit Grid Reference:  SN 54886 03732 (LIDAR) 

Bwlch Height:  102.6m (LIDAR) 

Bwlch Grid Reference:  SN 54795 03991 (LIDAR) 

Drop:  25.0m (LIDAR) 

 

Myrddyn Phillips (August 2024)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Safle Claddu Nant y Caws (SN 468 174) & (SN 469 174) and Cae Mawr (SN 462 175) - 28th significant height revision

Summit Relocations post for Safle Claddu Nant y Caws and Cae Mawr

 

There has been a Significant Height Revision to a hill that is now listed as a Dual Summit in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Cae Mawr (SN 462 175) and Safle Claddu Nant y Caws (SN 468 174) and (SN 469 174)

The criteria for the two listings that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

Dual Summit hills:

A hill classified as a Dual Summit is defined as one which has an extant natural summit coupled with that of a higher artificial summit, with the latter that can be described as stable in character.  In the main, these recent man-made constructions are the result of quarrying activities producing spoil tips, or as in this instance a landfill.  These recent man-made constructions are treated differently to ancient man-made constructions such as hill forts and tumuli, as if the latter are deemed stable and of an earthen character their age dictates that they can be viewed as being permanent in nature and are now effectively a part of the hill.  For those bagging Dual Summit hills, a visit to either the natural high point or the elevated man-made high point is sufficient to claim an ascent of the hill.  With the Dual Summit classification being a relatively new category and fist instigated in January 2018 for a Dual Summit Pedwar.

The name the hill is now listed by is Safle Claddu Nant y Caws for the higher man-made summit and Cae Mawr for the lower natural summit, and it is adjoined to the Mynydd Sylen group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and the two summits are positioned with the A48 road to their north and a minor road to their south-west, and has the town of Caerfyrddin (Carmarthen) towards the north-west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, the natural summit was included in the main P30 list with a 155m summit height, based on the spot height adjoined to a triangulation pillar positioned at SN 46405 17608 that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was then separated in to its two component parts, with the man-made summit listed with an estimated c 59m of drop, based on an estimated c 156m summit height positioned at SN 46909 17343 and an estimated c 97m bwlch height, with both heights based on interpolation of 5m contouring that appeared on the interactive mapping hosted on the OS Maps website.  With the lower natural summit listed with a 155 summit height and the bwlch between these two summits estimated as c 138m, which if separating these hills would give an estimated c 17m of drop.

However, it was not until LIDAR became available that the details for these summits could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Safle Claddu Nant y Caws (SN 468 174) and (SN 469 174)

LIDAR analysis gives the highest ground at the man-made summit as 163.8m positioned at SN 46899 17416 & SN 46900 17411, and this compared to its previously listed summit height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 163.8m and this was derived from LIDAR analysis, this is 7.8m higher than the previous listed summit height of c 156m, which was based on interpolation of its uppermost 155m ring contour that appeared on the interactive mapping hosted on the OS Maps website.

 

The full details for the hill are:

Group:  Mynydd Sylen

Name:  Safle Claddu Nant y Caws (artificial Dual Summit) and Cae Mawr (natural Dual Summit)

OS 1:50,000 map:  159

Summit Height (New Height):  163.8m (artificial Dual Summit) and 155.1m (natural Dual Summit) (LIDAR)

Summit Grid Reference:  SN 46899 17416 & SN 46900 17411 (artificial Dual Summit) and SN 46268 17566 (natural Dual Summit) (LIDAR)

Bwlch Height:  98.5m (LIDAR)

Bwlch Grid Reference:  SN 39491 11374 & SN 39493 11375 (LIDAR)

Drop:  65.3m (artificial Dual Summit) and 56.6m (natural Dual Summit) (LIDAR)

Dominance:  39.89% (artificial Dual Summit) and 36.50% (natural Dual Summit) (LIDAR)

 

Myrddyn Phillips (July 2024)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Allt Pendugoedydd (SN 749 311) - 27th significant height revision

Hill Reclassifications post for Allt Pendugoedydd

Significant Name Changes post for Allt Pendugoedydd

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Allt Pendugoedydd (SN 749 311)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Allt Pendugoedydd and this was confirmed by the Ordnance Survey series of Six-Inch maps, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A4069 road to its north-west and minor roads to its west and east, and has the village of Llangadog towards the south-west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as with only an uppermost 150m contour on the contemporary Ordnance Survey 1:25,000 Explorer map, it was considered not to meet the criteria then used for this sub category. 

Extract from the Ordnance Survey 1:25,000 Explorer map

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated against the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.  This mapping had many spot heights not on other publicly available maps and for this hill it had a 163m summit spot height positioned at SN 74989 31133.

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Allt Pendugoedydd (SN 749 311)

The height produced by LIDAR analysis to the summit of this hill is 162.4m positioned at SN 74992 31127, and this in relation to the detail on the contemporary Ordnance Survey 1:25,000 Explorer map comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 162.4m and this was derived from LIDAR analysis, this is 12.4m higher than the uppermost 150m contour on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Mynydd Du 

Name:  Allt Pendugoedydd 

OS 1:50,000 map:  146, 160

Summit Height (New Height):  162.4m (LIDAR) 

Summit Grid Reference:  SN 74992 31127 (LIDAR) 

Bwlch Height:  141.4m (LIDAR) 

Bwlch Grid Reference:  SN 75086 31369 (LIDAR) 

Drop:  21.0m (LIDAR) 

 

Myrddyn Phillips (April 2024)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Coed Uchaf (SJ 232 683) - 26th significant height revision

Hill Reclassifications post for Coed Uchaf

Summit Relocations post for Coed Uchaf

Significant Name Changes post for Coed Uchaf

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail produced by JoeNuttall in his surface analysis programme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Coed Uchaf (SJ 232 683)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Coed Uchaf, and it is adjoined to the Moel y Gamelin group of hills, which are situated in the north-eastern part of North Wales (Region A, Sub-Region A2), and it is positioned encircled by minor roads, with the A55 road farther to its north, the B5123 road farther to its west, the A541 road farther to its south and the A5119 road farther to its east, and has the town of Y Fflint (Flint) towards the north.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a summit height of c 160m positioned at SJ 232 686, based on the uppermost non-interpolated ring contour that appears on the contemporary Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated against the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.  This mapping had many spot heights not on other publicly available maps and for this hill it had a 162m summit spot height positioned at SJ 23209 68591.

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Coed Uchaf (SJ 232 683)

The height produced by LIDAR analysis to the summit of this hill is 161.7m positioned at SJ 23205 68344 as opposed to the 160.5m LIDAR height positioned at SJ 23205 68597.  This relocated summit position is not given an uppermost 160m ring contour on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 161.7m and this was derived from LIDAR analysis, this is 1.7m higher than the originally listed summit height of a non-interpolated c 160m and 0.3m lower than the 162m spot height that was positioned at SJ 23209 68591 on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

 

The full details for the hill are:

Group:  Moel y Gamelin 

Name:  Coed Uchaf 

OS 1:50,000 map:  117

Summit Height (New Height):  161.7m (LIDAR) 

Summit Grid Reference:  SJ 23205 68344 (LIDAR) 

Bwlch Height:  132.6m (LIDAR) 

Bwlch Grid Reference:  SJ 23101 68383 (LIDAR) 

Drop:  29.1m (LIDAR) 

 

Myrddyn Phillips (January 2024)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Bolton Beacon (SM 917 112) - 25th significant height revision

Significant Name Changes post for Bolton Beacon

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from detail produced by Joe Nuttall in his surface analysis progamme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Bolton Beacon (SM 917 112)

The criteria for the two listings that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Bolton Beacon and this was derived from a variety of Ordnance Survey maps, and it is adjoined to the Garn Fawr group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads, with the B4327 road farther to its north-west and the A4076 road farther to its east, and has the village of Johnston towards the east south-east.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a summit height of 110m, based on the spot height adjoined to a triangulation pillar positioned at SM 91681 11268 which appeared on the contemporary Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Bolton Beacon (SM 917 112)

The summit height produced by LIDAR analysis is 113.4m positioned at SM 91710 11288, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 113.4m and this was derived from LIDAR analysis, this is 3.4m higher than the originally listed summit height of 110m, which was based on the spot height adjoined to a triangulation pillar which appeared on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are: 

Group:  Garn Fawr 

Name:  Bolton Beacon 

OS 1:50,000 map:  157, 158

Summit Height (New Height):  113.4m (LIDAR) 

Summit Grid Reference:  SM 91710 11288 (LIDAR) 

Bwlch Height:  66.8m (LIDAR) 

Bwlch Grid Reference:  SM 89719 12333 & SM 89721 12333 (LIDAR) 

Drop:  46.7m (LIDAR) 

Dominance:  41.13% (LIDAR) 

 

Myrddyn Phillips (September 2023)

 

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Morris’ Meadow (SN 019 183) - 24th significant height revision

Summit Relocations post for Morris' Meadow

Significant Name Changes post for Morris' Meadow

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips.                            

LIDAR image of Morris' Meadow (SN 019 183)

The criteria for the two listings that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Morris’ Meadow and this was derived from the Tithe map, and it is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads, with the B4329 road farther to its west and the A40 road farther to its south, and has the town of Hwlffordd (Haverfordwest) towards the west south-west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a summit height of 122m, based on the spot height positioned at SN 02261 18187 which appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Morris Meadow (SN 019 183)

The summit height produced by LIDAR analysis is 119.4m positioned at SN 01923 18373, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 119.4m and this was derived from LIDAR analysis, this is 2.6m lower than the originally listed summit height of 122m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are: 

Group:  Mynydd Preseli 

Name:  Morris’ Meadow 

OS 1:50,000 map:  157, 158

Summit Height (New Height):  119.4m (LIDAR) 

Summit Grid Reference:  SN 01923 18373 (LIDAR) 

Bwlch Height:  65.2m (LIDAR) 

Bwlch Grid Reference:  SN 01619 20933 (LIDAR) 

Drop:  54.2m (LIDAR) 

Dominance:  45.41% (LIDAR) 

 

Myrddyn Phillips (May 2023)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Carn Gelli (SM 923 379) - 23rd significant height revision

Summit Relocations post for Carn Gelli

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data and LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Carn Gelli (SM 923 379)

The criteria for the list that this height revision applies to are:

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Carn Gelli, and it is adjoined to the Garn Fawr group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads with the A487 road farther to its south-east, and has the town of Abergwaun (Fishguard) towards the east south-east. 

Extract from the Ordnance Survey 1:25,000 Explorer map

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a summit height of 188m, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating; 191m on 2002 1:50,000 map. 

Extract from the Ordnance Survey 1:50,000 Landranger map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Carn Gelli (SM 923 379)

The height produced by LIDAR analysis to the summit of this hill is 190.7m positioned at SM 92313 37943, and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 190.7m and this was derived from LIDAR analysis, this is 2.7m higher than the originally listed summit height of 188m, which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Garn Fawr 

Name:  Carn Gelli 

OS 1:50,000 map:  157

Summit Height (New Height):  190.7m (LIDAR) 

Summit Grid Reference:  SM 92313 37943 (LIDAR) 

Bwlch Height:  128m (spot height) 

Bwlch Grid Reference:  SM 91953 38745 (spot height) 

Drop:  63m (LIDAR summit and spot height bwlch) 

 

Myrddyn Phillips (April 2023)

 

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Y Grongaer (SN 573 215 and SN 574 215) - 22nd significant height revision

Summit Relocations post for Y Grongaer

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Y Grongaer (SN 573 215 and SN 574 215)

The criteria for the two listings that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Y Grongaer, and it is adjoined to the Mynydd Mallaen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with the A40 road to its north, the B4297 road to its west, the B4300 road to its south and a minor road to its east, and has the town of Llandeilo towards the east.  

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a 143m summit height, based on the spot height that is positioned at SN 57326 21596 and appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Y Grongaer (SN 573 215 and SN 574 215)

The summit height produced by LIDAR analysis is 140.7m and is positioned at SN 57399 21574 and SN 57400 21575, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 140.7m and this was derived from LIDAR analysis, this is 2.3m lower than the originally listed summit height of 143m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Mynydd Mallaen 

Name:  Y Grongaer 

OS 1:50,000 map:  159

Summit Height (New Height):  140.7m (LIDAR) 

Summit Grid Reference:  SN 57399 21574 & SN 57400 21575 (LIDAR) 

Bwlch Height:  53.05m (LIDAR) 

Bwlch Grid Reference:  SN 57923 22123 (LIDAR) 

Drop:  87.6m (LIDAR) 

Dominance:  62.29% (LIDAR) 

 

Myrddyn Phillips (April 2022)

 

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Pt. 170.7m (SJ 193 018) - 21st significant height revision

Survey post for Pt. 170.7m

Significant Name Changes post for Pt. 170.7m

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Pt. 170.7m (SJ 193 018)

The criteria for the list that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

The hill is being listed by the point (Pt. 170.7m) notation as an appropriate name for it either through local enquiry and / or historic research has not been found by the author, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with a minor road to its north, the B4385 road to its west, the B4390 road to its south and the A483 road to its east, and has the village of Aberriw (Berriew) towards the south-west. 

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the main P30 list, with a 169m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR image of Pt. 170.7m (SJ 193 018)

The summit height produced by LIDAR analysis is 170.6m, but as the summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in 170.7m at SJ 19323 01898, it is this result that is being prioritised for listing purposes and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

The term Significant Height Revisions applies to any listed hill whose interpolated summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. 

The Trimble GeoXH 6000 gathering data at the summit of Pt. 170.7m (SJ 193 018)

Therefore, this hill’s new listed summit height is 170.7m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SJ 19323 01898 and is 1.7m higher than the previously listed summit height of 169m which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Carnedd Wen

Name:  Pt. 170.7m

OS 1:50,000 map:  136

Summit Height (New Height):  170.7m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SJ 19323 01898 (Trimble GeoXH 6000)

Bwlch Height:  132.5m (LIDAR)

Bwlch Grid Reference:  SJ 18115 01656 (LIDAR)

Drop:  38.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (June 2021)

 

 

 

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Banc (SN 568 757) - 20th significant height revision

Survey post for Banc

Significant Name Changes post for Banc

Summit Relocations post for Banc 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Banc (SN 568 757)

The criteria for the list that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Banc and this was derived from the Tithe map, and it is adjoined to the Elenydd group of hills which are situated in the western part of Mid and West Wales (Region B, Sub-Region B2), and it has the coast to its west and the A487 road to its east, and the village of Llanfarian towards the north-east. 

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 192m summit height, based on the spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 56695 75938. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR image of Banc (SN 568 757)

The summit height produced by LIDAR analysis indicated a relocation and as the summit has subsequently been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised in preference to the LIDAR height and position for this hill, resulting in 194.2m positioned at SN 56817 75750 and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

The term Significant Height Revisions applies to any listed hill whose interpolated summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. 

The Trimble GeoXH 6000 gathering data at the summit of Banc

Therefore, this hill’s new listed summit height is 194.2m and this was derived from a Trimble GeoXH 6000 survey, this is 2.2m higher than the previously listed 192m height which was based on the spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 56695 75938.

 

The full details for the hill are:

Group:  Elenydd 

Name:  Banc

OS 1:50,000 map:  135

Summit Height (New Height):  194.2m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SN 56817 75750 (Trimble GeoXH 6000)

Bwlch Height:  130.2m (LIDAR)

Bwlch Grid Reference:  SN 57845 73062 (LIDAR) 

Drop:  64.0m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (May 2021)

 

 

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Beddau (SO 185 977) - 19th significant height revision

Survey post for Beddau

 

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips. 

Beddau (SO 185 977)

The criteria for the list that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Beddau, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with the A483 road to its north-west, a minor road to its south-east and the B4386 road farther to its south-east, and has the village of Aberriw (Berriew) towards the north. 

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the main P30 list with a c 120m summit height taken from the uppermost contour that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

When the accompanying sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with c 36m of drop, based on an estimated c 124m summit height and an estimated c 88m bwlch height, based on interpolation of 5m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

Since the original compilation of this list there have been a number of Ordnance Survey maps made available online, some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website, whilst others are current and digitally updated such as the mapping on the WalkLakes website and the Magic Maps website. 

One of the mapping resources now available online is the Magic Maps website which hosts an interactive map originated from Ordnance Survey data.  This map has many spot heights not on other publicly available Ordnance Survey maps and for this hill a 126m spot height is given on the area of its summit. 

Extract from the Magic Maps website

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR image of Beddau (SO 185 977)

The summit height produced by LIDAR analysis is 126.0m positioned at SO 18549 97771, this is not a substantial height revision compared to some revised heights but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

The term Significant Height Revisions applies to any listed hill whose interpolated summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. 

The summit of Beddau

Therefore, this hill’s new listed summit height is 126.0m and this was derived from LIDAR analysis, this is 2.0m higher than the previously listed and estimated summit height of c 124m which was based on interpolation of the hill’s uppermost 120m ring contour on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Carnedd Wen

Name:  Beddau

OS 1:50,000 map:  136

Summit Height (New Height):  126.0m (LIDAR)

Summit Grid Reference:  SO 18549 97771 (LIDAR)

Bwlch Height:  87.9m (LIDAR)

Bwlch Grid Reference:  SO 18841 98344 (LIDAR)

Drop:  38.1m (LIDAR)

 

Myrddyn Phillips (March 2021)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

The Knoll (ST 424 904) - 18th significant height revision

Hill Reclassifications post for The Knoll

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of The Knoll (ST 424 904)

The criteria for the two listings that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol - The Dominant Hills of Wales - Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

The name the hill is listed by is The Knoll, and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the A48 road to its north and the M4 motorway to its south, and has the city of Casnewydd (Newport) towards the west south-west.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the main P30 list with a c 90m summit height, based on its uppermost contour that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:25,000 Explorer map

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with c 51m of drop, based on an estimated c 94m summit height based on interpolation of 5m contouring and a 43m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

LIDAR close up image of The Knoll

The summit height produced by LIDAR analysis is 101.9m positioned at ST 42467 90424, this is a substantial height revision compared to some revised heights and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. 

Therefore, this hill’s new listed summit height is 101.9m and this was produced by LIDAR analysis, this is 7.9m higher than its previously listed height of c 94m which was based on interpolation of its uppermost 90m ring contour on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Gwent Is Coed

Name:  The Knoll

OS 1:50,000 map:  171, 172

Summit Height (New Height):  101.9m (LIDAR)

Summit Grid Reference:  ST 42467 90424 (LIDAR)

Bwlch Height:  43.1m (LIDAR)

Bwlch Grid Reference:  ST 42135 90345 (LIDAR)

Drop:  58.7m (LIDAR)

Dominance:  57.66% (LIDAR)

Myrddyn Phillips (July 2020)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Chepstow Hill (ST 355 905) - 17th significant height revision

Summit Relocations post for Chepstow Hill

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Chepstow Hill (ST 355 905)

The criteria for the two listings that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol - The Dominant Hills of Wales - Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

The name the hill is listed by is Chepstow Hill and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Wysg (River Usk) to its north-west, the M4 motorway to its south and the A449 road to its east, and has the city of Casnewydd (Newport) towards the south-west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was listed with a 111m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:25,000 Explorer map

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and gives a 114m spot height on the summit area of this hill and positioned at ST 356 905.  This 114m spot height also appears on Ordnance Survey data available on the Magic Maps website.

Extract from the Magic Maps website

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

                                        

The summit height produced by LIDAR analysis is 116.6m positioned at ST 35547 90567, this is a substantial height revision compared to the original 111m listed summit height, and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. 

Therefore, this hill’s new listed summit height is 116.6m and this was produced by LIDAR analysis, this is 5.6m higher than its original listed height of 111m that appears as a spot height on the Ordnance Survey 1:25,000 Explorer map, and 2.6m higher than that of the online Vector Map Local.

The full details for the hill are:

Group:  Gwent Is Coed

Name:  Chepstow Hill

OS 1:50,000 map:  171

Summit Height (New Height):  116.6m (LIDAR)

Summit Grid Reference:  ST 35547 90567 (LIDAR)

Bwlch Height:  63.2m (LIDAR)

Bwlch Grid Reference:  ST 36979 90843 (LIDAR)

Drop:  53.4m (LIDAR)

Dominance:  45.76% (LIDAR)

Myrddyn Phillips (June 2020)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Coed Anghred Hill (SO 457 194) - 16th significant height revision

Summit Relocations post for Coed Anghred Hill

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Coed Anghred Hill (SO 457 194)

The criteria for the two listings that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

The name the hill is listed by is Coed Anghred Hill and it is adjoined to the Mynyddoedd Duon group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Mynwy (River Monnow) and the B4521 road to its north and the B4347 road to its west, and has the small village of Ynysgynwraidd (Skenfrith) towards the north.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 192m summit height based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SO 45823 19468.

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Coed Anghred Hill

The height produced by LIDAR analysis is 198.8m and is positioned at SO 45713 19487,  this is a substantial revision compared to some revised heights, and comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, this hill’s new listed summit height is 198.8m and this was derived from LIDAR analysis, this is 6.8m higher than the previously listed summit height of 192m which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group:  Mynyddoedd Duon

Name:  Coed Anghred Hill

OS 1:50,000 map:  161

Summit Height (New Height):  198.8m (LIDAR)

Summit Grid Reference:  SO 45713 19487 (LIDAR)

Bwlch Height:  128.8m (LIDAR)

Bwlch Grid Reference:  SO 44881 19181 (LIDAR)

Drop:  70.0m (LIDAR)

Dominance:  35.20%

Myrddyn Phillips (March 2020)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Garden Field (SO 180 383) - 15th significant height revision

Significant Name Changes post for Garden Field

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Garden Field (SO 180 383)

The criteria for the list that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The name the hill is now listed by is Garden Field and this derived from the Tithe map, and it is adjoined to the Mynyddoedd Duon group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C3), and it is encircled by minor roads with the Afon Gwy (River Wye) and the A438 road further to its north-west, and the village of Aberllynfi (Three Cocks) towards the south-west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was listed with a 168m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

The height produced by LIDAR analysis is 170.3m and is positioned at SO 18079 38331,  this is not a substantial revision compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, this hill’s new listed summit height is 170.3m and this was derived from LIDAR analysis, this is 2.3m higher than the previously listed summit height of 168m which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Mynyddoedd Duon

Name:  Garden Field

OS 1:50,000 map:  161

Summit Height (New Height):  170.3m (LIDAR)

Summit Grid Reference:  SO 18079 38331 (LIDAR)

Bwlch Height:  141.3m (LIDAR)

Bwlch Grid Reference:  SO 18629 38227 (LIDAR) 

Drop:  28.9m (LIDAR)

Myrddyn Phillips (March 2020)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Cae Cefn (ST 059 748) - 14th significant height revision

Significant Name Changes post for Cae Cefn

Hill Reclassifications post for Cae Cefn

There has been a Significant Height Revision to a hill that was listed in the 100m Twmpau, with the summit height and its location confirmed by a Leica GS15 survey conducted by John Barnard, Graham Jackson and Myrddyn Phillips which took place on the 4^th November 2013, and the bwlch height and its location, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

The Leica GS15 gathering data at the summit of Cae Cefn

The criteria for the list that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

LIDAR image of Cae Cefn (ST 059 748)

The name the hill is now listed as is Cae Cefn and this derived from the Tithe map, and it is adjoined to the Bro Morgannwg group of hills, which are situated in the southern part of South Wales (Region C, Sub-Region C2), and it is positioned with the A48 road to its south-east and minor roads to its west, north and east, has the city of Caerdydd (Cardiff) towards the east and the town of Y Bont-faen (Cowbridge) to the west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was listed with a 140m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.  However, as the 140m spot height is placed at the top of a covered reservoir and as these structures are considered recent man-made constructs and as Tair Onnen vied for being the higher hill, both hills were surveyed using a Leica GS15, resulting in:

Cae Cefn (ST 05910 74886):  136.2m (natural ground at base of covered reservoir)

Tair Onnen (ST 03660 73979):  137.3m

When LIDAR became available the details for these two hills were re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.  The LIDAR summit details are given below:

Cae Cefn (ST 05915 74885):  136.4m (natural ground at base of covered reservoir)

Tair Onnen (ST 03661 73979):  137.4m

Extract from the Ordnance Survey 1:25,000 Explorer map

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

The height produced by the Leica GS15 survey is 136.2m and is positioned at ST 05910 74886, this revised height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, or other GNSS equipment, or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, this hill’s new listed summit height is 136.2m and this is to natural ground at the base of a covered reservoir and positioned at ST 05910 74886,  this is 3.8m lower than the previously listed summit height of 140m which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Bro Morgannwg

Name:  Cae Cefn

OS 1:50,000 map:  170

Summit Height (New Height):  136.2m (Leica GS15)

Summit Grid Reference:  ST 05910 74886 (Leica GS15)

Bwlch Height:  116.25m (LIDAR)

Bwlch Grid Reference:  ST 04273 74542 (LIDAR)

Drop:  19.9m (Leica GS15 summit and LIDAR bwlch)

Myrddyn Phillips (October 2019)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Wenvoe Quarry (ST 131 741) - 13th significant height revision

Significant Name Changes post for Wenvoe Quarry

Summit Relocations post for Wenvoe Quarry

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height and its position confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR summit image of Wenvoe Quarry (ST 131 741)

The criteria for the two listings that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name the hill is now listed by is Wenvoe Quarry and it is adjoined to the Bro Morgannwg group of hills, which are situated in the southern part of South Wales (Region C, Sub-Region C2), and it is positioned with a number of A roads encircling it with the A4232 to its north and east, the A4050 to its west and the A4055 further to its south-east, and has the city of Caerdydd (Cardiff) towards the north-east.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a c 115m summit height, based on the uppermost contour on contemporary Ordnance Survey 1:25,000 Explorer maps.

When this list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 117m summit height based on interpolation of the uppermost 115m contour on the Ordnance Survey 1:25,000 Explorer map, with this summit height later being changed to an estimated c 118m.

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.  

The height produced by LIDAR analysis is 123.4m and is positioned at ST 13189 74189,  this is a substantial revision compared to some revised heights, and comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, this hill’s new listed summit height is 123.4m and this was derived from LIDAR analysis, this is 5.4m higher than the previously listed summit height of c 118m which was based on an estimated height from interpolation of its uppermost 115m contour on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Bro Morgannwg

Name:  Wenvoe Quarry

OS 1:50,000 map:  171

Summit Height (New Height):  123.4m (LIDAR)

Summit Grid Reference:  ST 13189 74189 (LIDAR)

Bwlch Height:  66m (spot height)

Bwlch Grid Reference:  ST 12669 74393 (spot height) 

Drop:  57m (LIDAR summit and spot height bwlch)

Dominance:  46.51% (LIDAR summit and spot height bwlch)

Myrddyn Phillips (October 2019)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Woodlake Park (ST 343 997) - 12th significant height revision

Significant Name Changes post for Woodlake Park

Summit Relocations post for Woodlake Park

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Woodlake Park (AT 343 997)

The criteria for the two listings that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name the hill is listed by is Woodlake Park and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is positioned above the Llandegfedd Reservoir which is to its west, and has the town of Pont-y-pŵl (Pontypool) towards its west and Brynbuga (Usk) towards its east.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 147m summit height, based on the spot height positioned at ST 340 994 that appears on the Ordnance Survey 1:50,000 Landranger map, with the 1:25,000 Explorer map having no spot height.

The details for this hill were re-evaluated when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online, and as this map gives a 149m spot height positioned at ST 34341 99786, the summit of this hill was relocated.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

The height produced by LIDAR analysis is 150.7m positioned at ST 34335 99793,  this is not a substantial revision compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, this hill’s new listed summit height is 150.7m and this was derived from LIDAR analysis, this is 1.7m higher than the previously listed summit height of 149m which was derived from the spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website. 

  

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Woodlake Park

OS 1:50,000 map:  171

Summit Height (New height):  150.7m (LIDAR)

Summit Grid Reference:  ST 34335 99793 (LIDAR)

Bwlch Height:  91.5m (LIDAR)

Bwlch Grid Reference:  ST 33405 01033 (LIDAR)

Drop:  59.3m (LIDAR)

Dominance:  39.31%

Myrddyn Phillips (August 2019)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

The Mount (ST 258 848) - 11th significant height revision

Significant Name Changes post for The Mount

Summit Relocations post for The Mount

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height derived from the OS Trig Database and the bwlch height derived from interpolation of 5m contouring.

The criteria for the two listings that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name of the hill is The Mount, and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it has minor roads to its north-west and north-east and the M4 motorway to its south, and is positioned between the city of Caerdydd (Cardiff) to the south-west and Casnewydd-ar-Wysg (Newport) to the north-east.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 124m summit height, based on the spot height positioned at ST 25276 84738 that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating that the Ordnance Survey 1:50,000 Landranger map dated 1986 has a 127m spot height adjoined to a triangulation pillar and which is positioned at ST 25869 84831.  As heights on 1:25,000 scale mapping were prioritised in this list over those on 1:50,000 scale mapping this hill’s summit was listed to where the 124m spot height appears on the 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:25,000 Explorer map

Since publication of these P30 lists on Geoff Crowder’s v-g.me website the heights on different scaled Ordnance Survey maps can be cross referenced against a number of sources that are now available online, and 1:25,000 map data is no longer prioritised for summit heights over that of 1:50,000 map data, each is now assessed individually.  Therefore, the 127m height given to the triangulation pillar is now prioritised for the summit height of this hill, this is not a substantial revision compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, this hill’s new listed summit height is 127m and this was derived from the 127.247m flush bracket height adjoined to a triangulation pillar that once stood on the summit of this hill and which was destroyed in September 1985, this is 3m higher than the previously listed summit height of 124m which was derived from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

  

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  The Mount

OS 1:50,000 map:  171

Summit Height (New height):  127m

Summit Grid Reference:  ST 25868 84839

  

Bwlch Height:  c 66m

Bwlch Grid Reference:  ST 24800 87551

Drop:  c 61m

Dominance:  48.03%

Myrddyn Phillips (August 2019)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Bryn Bach (SS 903 875) - 10th significant height revision

Hill Reclassifications post for Bryn Bach

Significant Name Changes post for Bryn Bach

Summit Relocations post for Bryn Bach

There has been a Significant Height Revision to a hill that is now listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Bryn Bach

The criteria for the list that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The name of the hill is Bryn Bach, and this was derived from the Ordnance Survey One-Inch ‘Old Series’ map and it is this name that the hill is now listed by, and it is adjoined to the Cymoedd Morgannwg group of hills, which are situated in the central part of South Wales (Region C, Sub-Region C2), and is positioned with the A4063 road and the Afon Llynfi to its south-west and the A4064 road and the Afon Garw to its south-east, and has the small community of Betws towards the south. 

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the Hills to be surveyed sub list that accompanied the main P30 list, as it did not meet the criteria then used. 

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 31m of drop, based on an estimated summit height of c 164m and an estimated bwlch height of c 133m, with both heights based on interpolation of 10m contouring on the Ordnance Survey 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:25,000 Explorer map

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website became available online; this mapping is entitled the Interactive Coverage Map.  This mapping gives a 164m summit spot height and as it has 5m contour intervals it enabled a better assessment for an interpolated value for the height of the bwlch.  It also has a 133m spot height at a junction of roads at the area of this hill’s bwlch, with interpolation favouring a different position for the critical bwlch and an estimated height of c 133m, with these values giving this hill c 31m of drop.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.  

The summit height produced by LIDAR analysis is 167.0m, this is not a substantial revision compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new listed summit height is 167.0m and this was produced by LIDAR analysis, this is 3m higher than the 164m spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map.

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Bryn Bach

OS 1:50,000 map:  170

Summit Height (New height):  167.0m (LIDAR)

Summit Grid Reference:  SS 90364 87431 (LIDAR)

  

Bwlch Height:  135.2m (LIDAR)

Bwlch Grid Reference:  SS 90511 87849 (LIDAR)

Drop:  31.9m (LIDAR)

Myrddyn Phillips (June 2019)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Coed Cae Bach (SS 855 841) - 9th significant height revision

Hill Reclassifications post for Coed Cae Bach

Significant Name Changes post for Coed Cae Bach

There has been a Significant Height Revision to a hill that is now listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Coed Cae Bach

The criteria for the list that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The name of the enclosed land that once comprised ground where the summit of this hill is situated is Coed Cae Bach, and this was derived from the Tithe map and it is this name that the hill is now listed by.  The hill is adjoined to the Cymoedd Morgannwg group of hills, which are situated in the central part of South Wales (Region C, Sub-Region C2), and it forms a part of landscaped ground that once made up the Margam opencast mine, and is encircled by minor roads to its north, west and east and has the B4281 road and the small communities of Cefn Cribwr and Kenfig Hill towards its south.

This hill did not appear in the original 100m height band of Welsh P30 hills when they were published on Geoff Crowder’s v-g.me website as contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps of the day showed the opencast mine without any ring contours of note.

Extract from the Ordnance Survey 1:25,000 Explorer map

This area was re-examined when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals and for the majority of land comprising old mine workings it shows present day contours, as opposed to the blank space showed on the counterparts of the 1:50,000 Landranger and 1:25,000 Explorer maps.

Extract from the OS Maps website

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Coed Cae Bach

The summit height produced by LIDAR analysis is 102.3m, this is a substantial revision compared to some revised heights, and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new listed summit height is 102.3m and this was produced by LIDAR analysis, this is 34m higher than a 68m spot height that appears on the southern periphery of this hill on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map.

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Coed Cae Bach

OS 1:50,000 map:  170

Summit Height (New height):  102.3m (LIDAR)

Summit Grid Reference:  SS 85525 84189 (LIDAR) 

Bwlch Height:  72.0m (LIDAR)

Bwlch Grid Reference:  SS 85129 84233 (LIDAR)

Drop:  30.4m (LIDAR)

Myrddyn Phillips (June 2019)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Pedwar Erw (SS 864 837) - 8th significant height revision

Hill Reclassifications post for Pedwar Erw

Significant Name Changes post for Pedwar Erw

There has been a Significant Height Revision to a hill that is now listed in the 100m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Pedwar Erw

The criteria for the list that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The name of the enclosed land that once comprised ground where the summit of this hill is situated is Pedwar Erw, and this was derived from the Tithe map and it is this name that the hill is now listed by.  The hill is adjoined to the Cymoedd Morgannwg group of hills, which are situated in the central part of South Wales (Region C, Sub-Region C2), and it forms a part of landscaped ground that once made up the Margam opencast mine, and is encircled by minor roads to its north, west and east and has the B4281 road and the small communities of Cefn Cribwr and Kenfig Hill towards its south.

This hill did not appear in the original 100m height band of Welsh P30 hills when they were published on Geoff Crowder’s v-g.me website as contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps of the day showed the opencast mine without any ring contours of note.

Extract from the Ordnance Survey 1:25,000 Explorer map

This area was re-examined when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals and for the majority of land comprising old mine workings it shows present day contours, as opposed to the blank space showed on the counterparts of the 1:50,000 Landranger and 1:25,000 Explorer maps.

Extract from the OS Maps website

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Pedwar Erw

The summit height produced by LIDAR analysis is 131.0m, this is a substantial revision compared to some revised heights, and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new listed summit height is 131.0m and this was produced by LIDAR analysis, this is 31m higher than the highest contour that appears on the Ordnance Survey 1:25,000 Explorer map, and this is only a partial contour as it soon disappears in to the blank space associated with mine workings that appears on many contemporary Ordnance Survey maps.

The full details for the hill are:

Group:  Cymoedd Morgannwg

Name:  Pedwar Erw

OS 1:50,000 map:  170

Summit Height (New height):  131.0m (LIDAR)

Summit Grid Reference:  SS 86413 83767 (LIDAR)

Bwlch Height:  98.4m (LIDAR)

Bwlch Grid Reference:  SS 86635 84031 (LIDAR)

Drop:  32.5m (LIDAR)

Myrddyn Phillips (May 2019)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Llys y Gwynt (SH 779 728) - 7th significant height revision

Survey post for Llys y Gwynt

Significant Name Changes post for Llys y Gwynt

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height and its location, and the drop of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000, both conducted by Myrddyn Phillips with the latter taking place on the 10^th October 2018.

Llys y Gwynt (SH 779 728)

The criteria for the two lists that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height with 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name of the hill is Llys y Gwynt, and it is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and is positioned with the B5106 to its west, the B5279 to its south and the Afon Conwy (River Conwy) to its east, and has the town of Conwy to its north.

When interpolated heights and drop values were added to the original Welsh 100m P30 list that was published on Geoff Crowder’s v-g.me website, this hill was listed with an estimated c 116m summit height based on interpolation of its uppermost 110m contour ring that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.  LIDAR analysis for this hill was closely followed by the survey of its summit with the Trimble GeoXH 6000. 

LIDAR image of Llys y Gwynt

The summit height produced by the Trimble GeoXH 6000 survey is 120.6m,  this is a substantial revision when compared to some revised heights, and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new listed summit height is 120.6m and this was produced by surveying with the Trimble GeoXH 6000, this is 4.6m higher than its previously listed height of c 116m which was based on interpolation of its uppermost 110m ring contour that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, however this new height is in accordance with the 5m contouring on OS Maps.

Extract from OSMaps showing an uppermost 120m ring contour

The full details for the hill are:

Group:  Carneddau

Name:  Llys y Gwynt

OS 1:50,000 map:  115

Summit Height (New height):  120.6m (converted to OSGM15)

Summit Grid Reference:  SH 77982 72884  

Bwlch Height:  50.7m (LIDAR)

Bwlch Grid Reference:  SH 76137 71943 (LIDAR)

Drop:  70.0m (Trimble summit and LIDAR bwlch)

Dominance:  58.00% (Trimble summit and LIDAR bwlch)

For details on the summit survey of this hill

Myrddyn Phillips (March 2019)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Bryn Maelgwyn (SH 795 805) - 6th significant height revision

Survey post for Bryn Maelgwyn

There has been a Significant Height Revision to a hill that is listed in the 100m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from a Trimble GeoXH 6000 summit survey and LIDAR bwlch analysis conducted by Myrddyn Phillips. 

LIDAR image of Bryn Maelgwyn (SH 795 805)

The criteria for the two listings that this height revision applies to are:

100m Twmpau - Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

100m Twmpau by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Bryn Maelgwyn and it is adjoined to the Mynydd Hiraethog group of hills, which are situated in the northern part of North Wales (Region A, Sub-Region A2), and it is positioned with the B5115 road to its north, the A470 road to its west and minor roads to its south-east and north-east, and has the town of Llandudno towards the north-west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a non-interpolated summit height of c 100m, based on the uppermost contour that appears on the Ordnance Survey 1:25,000 Explorer map.  

Extract from the Ordnance Survey 1:25,000 Explorer map

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 43m of drop, based on an estimated c 106m summit height and an estimated c 63m bwlch height, with both heights based on interpolation of 5m contouring that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

The summit height produced by the Trimble GeoXH 6000 survey is 102.1m positioned at SH 79580 80540, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

The Trimble GeoXH 6000 gathering data from the summit of Bryn Maelgwyn

Therefore, the new listed summit height of this hill is 102.1m and this was derived from a Trimble GeoXH 6000 survey, this is 3.9m lower than the previously listed summit height of c 106m, which was based on interpolation of 5m contouring on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

The full details for the hill are:

Group:  Mynydd Hiraethog 

Name:  Bryn Maelgwyn

OS 1:50,000 map:  115

Summit Height (New Height):  102.1m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 79580 80540 (Trimble GeoXH 6000) 

         

Bwlch Height:  63.5m (LIDAR)

Bwlch Grid Reference:  SH 79893 80558 (LIDAR)

Drop:  38.5m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Dominance:  37.76% (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Myrddyn Phillips (January 2016)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

The Pimple (SJ 299 472) - 5th significant height revision

Survey post for The Pimple

Hill Reclassifications post for The Pimple

Summit Relocations post for The Pimple

Significant Name Changes post for The Pimple


There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to the listing of the 100m Twmpau, with these details being retrospective as the survey that resulted in this height revision was conducted on the 2oth October 2015.

The criteria for the listing that this height revision affects are:

100m Twmpau - These are the Welsh hills at or above 100m and below 200m in height that have a minimum drop of 30m.  The word Twmpau is an acronym for thirty welsh metre prominences and upward.  The criteria for 100m Sub-Twmpau status are all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop. 

The name of the hill is The Pimple; this is a locally known name which was given me when I made enquiries during the survey for the bwlch position of the hill.  The hill remains unnamed on Ordnance Survey maps and its locally known name relates directly to the past industrial heritage of the hill, as its summit is made of mining waste that is now stabilised and grassed over.  The uppermost part of the summit is relatively small in area and squat in shape, and resembles a pimple as it sits upon another elevated part of the hill.

The hill is situated in the eastern part of the Moel y Gamelin range of hills, and is positioned above the small community of Pentre Bychan which is adjacent to the larger community of Rhosllanerchrugog.

The hill can be accessed from its west where a public footpath traverses the course of the valley where its bwlch is positioned.  However, permission should be sought for those wishing to visit as the summit is not on designated open access land.  When I visited I asked permission to do so and was kindly directed to the best ascent route.

Prior to the survey with the Trimble GeoXH 6000 this hill was not classified but its summit position was indicated to be at SJ 30075 47320, this is where a 154m spot height appears on Ordnance Survey 1:25,000 Explorer maps, with a 23m difference in height compared to the  131m summit spot height on the Ordnance Survey 1:50,000 Landranger map.   The latter spot height is positioned in a field which had been ploughed and probably seeded when I visited.  However there is also high ground to the south-west of where the 154m spot height appears on the ground and each respective point was surveyed, with the following results:

                                                                                                                                 

South-western high point (The Pimple):  153.5m (converted to OSGM15) at SJ 29984 47262

North-eastern high point (154m spot height in field):  153.1m (converted to OSGM15) at SJ 30071 47279

The 153.5m (converted to OSGM15) summit height is not a dramatic height revision when compared to the 154m spot height, but the new summit position does not possess any ring contours on current Ordnance Survey maps and therefore meets the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the surveyed height produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.

Although this hill’s new summit height of 153.5m (converted to OSGM15) is only 0.5m different from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, the hill’s summit position has now been established and this is 8.5m higher than the 145m uppermost contour ring shown on the 1:25,000 map for where the summit of the hill is positioned.

The full details for the hill are:

Cardinal Hill:  Moel y Gamelin

Summit Height (New Height):  153.5m (converted to OSGM15)

Name:  The Pimple

OS 1:50,000 map:  117

Summit Grid Reference:  SJ 29984 47262 

         

Drop:  25.2m (converted to OSGM15)

Gathering data at the summit of The Pimple which resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips (November 2015)






Mapping Mountains - Significant Height Revisions - 100m Twmpau

Bersham Bank (SJ 311 481) - 4th significant height revision

Survey post for Bersham Bank

Hill Reclassification post for Bersham Bank

Significant Name Changes post for Bersham Bank

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill that is now listed in the 100m Twmpau (thirty welsh metre prominences and upward), with these details being retrospective as the survey that resulted in this height revision was conducted on 13^th October 2015.  With the criteria for 100m Twmpau status being all Welsh hills at or above 100m and below 200m in height that have a minimum 30m of drop.

The name of the hill is Bersham Bank; with this being the preferred locally known name for the hill and which was given me when I made enquiries after my ascent (see Significant Name Changes).  There is no name for the hill on current maps but ‘Colliery (disused)’ appears on the Ordnance Survey 1:25,000 Explorer map where the hill is situated.  As the Ordnance Survey detail implies, this hill is the relic of coal waste which was deposited from the workings of the Bersham Colliery which closed its operations in December 1986.

Bersham Bank is situated in the Moel y Gamelin range of hills, and is positioned on the southern outskirts of Rhostyllen, which is a south-western suburb of Wrecsam (Wrexham).  There is a circuitous path on the southern and eastern middle section of the hill; this can be accessed from a road to its east that is adjacent to an industrial estate.  Beside the road is a perimeter fence seemingly barring entrance to a path on the lower slopes of the hill, however, one section of the six foot high fence has been toppled over giving access to the public, including local people, who I was told occasionally walk up the hill.

The hill had no classification prior to the survey with the Trimble GeoXH 6000 as although it is prominent and rises almost directly above the A 483; it possesses no contour rings on current Ordnance Survey maps, except for those at its bwlch and these are between 100m – 105m, with the height of the bwlch estimated as being c 103m, with the summit height produced by the survey with the Trimble GeoXH 6000 being 153.6m (converted to OSGM15).

Although this hill does not possess any summit contours on Ordnance Survey mapping, there are two hills created from coal waste that are relatively near to Bersham Bank that do possess separate ring contours, these are situated at SJ 311 469 and SJ 300 473. 

Therefore this hill’s new summit height is 153.6m (converted to OSGM15), as no summit contours exist for the hill this is a dramatic 48.6m increase in height compared to its uppermost hill to hill bwlch contour of 105m.

The full details for the hill are:

Cardinal Hill:  Moel y Gamelin

Summit Height (New Height):  153.6m (converted to OSGM15)

Name:  Bersham Bank

OS 1:50,000 map:  117

Summit Grid Reference:  SJ 31159 48116

   

Drop:  c 51m

Gathering data from the summit of Bersham Bank which resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips (November 2015)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Bryn Mawr (SJ 251 190) - 3rd significant height revision

Survey post for Bryn Mawr


There has been a Significant Height Revision to a hill listed in the 100m Twmpau and Y Trechol - The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted on 8^th August 2015.

The criteria for the two listings that this height revision affects are:

100m Twmpau - These are the Welsh hills at or above 100m and below 200m in height that have a minimum drop of 30m.  The word Twmpau is an acronym for thirty welsh metre prominences and upward. 

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence  equal or exceed half that of their absolute height.

The name of the hill is Bryn Mawr and it is situated in the lower hills of the Carnedd Wen range, and is positioned above the small community of Four Crosses which is situated beside the Afon Efyrnwy (River Vyrnwy) and part of the Montgomeryshire Canal.

The hill was surveyed in the company of Alex Cameron during a multi hill bagging day when the weather was set fine and we visited nine P30 Twmpau hills with seven of them being Trimbled.

Access to Bryn Mawr is good from the west of its summit, as there is sufficient parking close to a gate that accesses a field to another gate which leads on to the hill.  However, the upper section is overgrown and the ancient earthen embankments of its hill fort are now immersed in long grass, nettles and brambles.  The summit is easily identified and the hill is recommended as there is a peaceful ambiance to it.

The hill has a 170m uppermost contour ring on  Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, with the latter having contour intervals at 5m.  Prior to the survey with the Trimble GeoXH 6000 the hill had been listed with an estimated summit height of c 174m based on the dimensions of the uppermost contour in relation to the steepness of the surrounding ground, with the height resulting from the survey with the Trimble GeoXH 6000 being 178.1m (converted to OSGM15).

Therefore this hill’s new summit height is 178.1m (converted to OSGM15) which is 4.1m higher than its previously estimated height of c 174m and 8.1m higher than its uppermost ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill:  Carnedd Wen

Summit Height (New Height):  178.1m (converted to OSGM15)

Name:  Bryn Mawr

OS 1:50,000 map:  126

Summit Grid Reference:  SJ 25117 19054

  

Drop:  90m

Dominance:  50.53%

Gathering data from the summit of Bryn Mawr which resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips (September 2015)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Y Gaer (SJ 204 155) - 2nd significant height revision

Survey post for Y Gaer

2nd Survey post for Y Gaer

Summit Relocations post for Y Gaer

The summit of this hill has been re-surveyed with the Trimble GeoXH 6000 and its bwlch analysed by LIDAR, resulting in a 129.3m summit at SJ 20417 15566 and a 91.2m bwlch at SJ 21177 15977, giving 38.2m drop and 29.51% dominance.  The above values are taken to remaining natural ground at the base of the covered reservoir at the summit and the raised road at the bwlch, with the below post retained in its original format for historical purposes.

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill that is listed in the 100m Twmpau (thirty welsh metre prominences and upward), with these details being retrospective as the survey that resulted in this height revision was conducted on 8^th August 2015.  With the criteria for 100m Twmpau status being all Welsh hills at or above 100m and below 200m in height that have a minimum 30m of drop.

The name of the hill is Y Gaer and it is situated in the Carnedd Wen range, and is positioned above the small community of Trefnanney which is beside the Afon Efyrnwy (River Vyrnwy) and the Dyffryn Meifod.

Y Gaer was surveyed in the company of Alex Cameron during a multi hill bagging day when we had glorious weather and visited nine P30 Twmpau hills with seven of them being Trimbled.

The hill has two uppermost 125m ring contours on Ordnance Survey 1:25,000 Explorer maps, these are bisected by a lane that follows this hill’s summit ridge in a south-west to north-east direction.  It is from the top of this narrow lane that easy access to the high point of the hill can be found.

The larger of the two uppermost ring contours is positioned to the west of the smaller one, and it is the larger ring contour where the remains of an ancient earthen embankment is indicated on Ordnance Survey maps.  It is this ancient hill fort that gives the hill its name.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was estimated as being c 129m based on the dimension of the uppermost westerly 125m contour ring against the steepness of ground as indicated by contours on this hill’s northern, western and southern slopes.

However, the summit of this hill now possesses a covered reservoir which is indicated as a small round circle on Ordnance Survey maps, and as a number of P30s comprising many walks took place on the day of this hill's survey the lay of land was quickly judged and the Trimble GeoXH 6000 placed on land that probably forma a part of the covered reservoir.  If the hill is visited again the land will be re-assessed, but until then the height and position of the summit is being taken as that produced by the Trimble, a second visit would also give chance to survey the highest point of the easterly contour.

The 130.5m (converted to OSGM15) height produced by the Trimble GeoXH 6000 is not a dramatic height revision when compared to this hill’s previously listed height of c 229m, but as the contours on the Ordnance Survey 1:25,000 Explorer map are at 5m intervals it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the height surveyed with the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.

Therefore this hill’s new summit height is 130.5m (converted to OSGM15) which is 1.5m higher than its previously estimated height and 5.5m higher than its uppermost ring contour on current Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill:  Carnedd Wen

Summit Height (New Height):  130.45m (converted to OSGM15)

Name:  Y Gaer

OS 1:50,000 map:  126

Summit Grid Reference:  SJ 20413 15563

  

Drop:  c 39m

Gathering data from the summit of Y Gaer which resulted in this hill's significant height revision

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips (September 2015)

Mapping Mountains - Significant Height Revisions - 100m Twmpau

Bryn y Beili (SJ 235 643) - 1st significant height revision

Survey post for Bryn y Beili

Hill Reclassifications post for Bryn y Beili


There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to the listing of the 100m Twmpau (thirty welsh metre prominences and upward), with these details being retrospective as the survey that resulted in this height revision was conducted on 8^th April 2014.  With the criteria for 100m Twmpau status being all Welsh hills at or above 100m and below 200m in height that have a minimum 30m of drop.

The name of the hill is Bryn y Beili (Bailey Hill in English) and it is situated in the Bryniau Clwyd range of hills and is positioned in the town centre of Yr Wyddgrug (Mold), which is situated in north-east Wales.  The survey was conducted in the company of Mark Trengove over two days, three weeks apart, and it was Mark who proposed that this hill was a candidate for becoming a new P30, his inclination proved correct.  With the first survey concentrating on the bwlch and which resulted in an unfortunate incident when the Trimble wrestled with a car and was run over, whilst the second survey concentrated on the summit of the hill.

The hill can be accessed from the top of the High Street in Yr Wyddgrug (Mold), although the hill is prominent within the town it is almost hidden from view as it rises behind the former Pendref Chapel and is surrounded by a high wall, trees and shrubs.

The summit height of Bryn y Beili has been increased from its current Ordnance Survey map height, as prior to the survey with the Trimble GeoXH 6000 the hill was not listed as it only had an uppermost ring contour of 130m on Ordnance Survey 1:25,000 Explorer maps, with a 135m spot height appearing on lower ground in the centre of a bowling rink on the Ordnance Survey enlarged mapping hosted on the Geograph website.  The hill's new summit height is 143.0m (converted to OSGM15) which is 8.0m higher than the 135m spot height.

The full details for the hill are:

Cardinal Hill:  Moel y Gamelin

Summit Height (New Height):  143.0m (converted to OSGM15)

Name:  Bryn y Beili

OS 1:50,000 map:  117

Summit Grid Reference:  SJ 23544 64367

  

Drop:  31.5m (converted to OSGM15)

Bryn y Beili, a new P30 and a hill whose height has been significantly revised

For details on the survey that significantly revised the summit height of this hill

Myrddyn Phillips (August 2015)