Mapping Mountains – Significant Height Revisions – 30-99m Twmpau

30-99m Twmpau – Significant Height Revisions

The 30-99m Twmpau (thirty welsh metre prominences and upward) are the Welsh hills at or above 30m and below 100m in height that have a minimum drop of 30m.  Accompanying the main P30 list are two sub lists entitled the 30-99m Sub-Twmpau with the qualification to this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the Double Sub-Twmpau with the qualification to this sub category being all Welsh hills at or above 20m and below 30m 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 lists appear below presented chronologically in receding order.

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Cae Cwarre (SN 506 209) - 35th significant height revision

Significant Name Changes post for Cae Cwarre

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Cae Cwarre (SN 506 209)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m Twmpau by Myrrdyn 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 Cae Cwarre and this was derived from the Tithe map, 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, a minor road to its west and the B4300 road to its south, and has the small community of Llanegwad towards the east north-east.

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 summit height of 68m based on the spot height that appears on 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-evaluated and it was listed with an estimated c 34m of drop, based on the 68m summit spot height and an estimated c 34m bwlch height, based on interpolation of 10m contouring between 30m – 40m, with these values giving this hill 50% dominance. 

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.

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive 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 5m contouring, resulting in the bwlch height being amended to an estimated c 37m based on interpolation of contours between 35m – 40m, resulting in this hill being listed with an estimated c 31m of drop and 45.59% 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 Cae Cwarre (SN 506 209)

The summit height produced by LIDAR analysis is 70.9m and is positioned at SN 50644 20918, 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 70.9m and this was derived from LIDAR analysis, this is 2.9m higher than the previously listed summit height of 68m, 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:  Mynydd Mallaen 

Name:  Cae Cwarre 

OS 1:50,000 map:  159

Summit Height (New Height):  70.9m (LIDAR) 

Summit Grid Reference:  SN 50644 20918 (LIDAR)               

Bwlch Height:  36.1m (LIDAR) 

Bwlch Grid Reference:  SN 51854 21860 (LIDAR) 

Drop:  34.8m (LIDAR) 

Dominance:  49.04% (LIDAR) 

 

Myrddyn Phillips (May 2022)

 

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Castell y Dryslwyn (SN 554 203) - 34th significant height revision

Significant Name Changes post for Castell y Dryslwyn

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Castell y Dryslwyn (SN 554 203)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m 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 Castell y Dryslwyn 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 a minor road to its north, the B4297 road to its west and the Afon Tywi to its south, and has the town of Llandeilo towards the east north-east.

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 summit height of 71m based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger map. 

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

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 50m of drop, based on an estimated c 76m summit height based on interpolation of the uppermost 75m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map, and an estimated c 26m bwlch height based on interpolation of 5m contouring between 25m – 30m. 

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 Castell y Dryslwyn (SN 554 203)

The summit height produced by LIDAR analysis is 72.4m and is positioned at SN 55420 20301, 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 72.4m and this was derived from LIDAR analysis, this is 3.6m lower than the previously listed summit height of c 76m, which was based on interpolation of 5m contouring that appear on the Ordnance Survey 1:25,000 Explorer map, and 1.4m higher than its originally listed summit height which was based on the 71m spot height that appears on the Ordnance Survey 1:50,000 Landranger map.

 

The full details for the hill are:

Group:  Mynydd Mallaen 

Name:  Castell y Dryslwyn 

OS 1:50,000 map:  159

Summit Height (New Height):  72.4m (LIDAR) 

Summit Grid Reference:  SN 55420 20301 (LIDAR)               

Bwlch Height:  25.3m (LIDAR) 

Bwlch Grid Reference:  SN 55696 20577 (LIDAR) 

Drop:  47.1m (LIDAR) 

Dominance:  65.02% (LIDAR) 

 

Myrddyn Phillips (May 2022)

 

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Allt Dan Tŷ Mawr (SN 520 228) - 33rd significant height revision

Hill Reclassifications post for Allt Dan Tŷ Mawr

  

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Allt Dan Tŷ Mawr (SN 520 228)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30m-99m 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 Allt Dan Tŷ Mawr 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 minor roads to its north, west and south, and the A40 road to its south-west, and has the town of Llandeilo towards the east.

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 Hills to be surveyed sub list, as it was considered not to meet the criteria then used in the main P30 category.

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 29m of drop, based on an estimated c 67m summit height and the 38m bwlch spot height 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

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.

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive 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 69m summit spot height positioned at SN 51824 22804, and when coupled with the 38m bwlch spot height these values gave this hill 31m of drop and 44.93% 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 Allt Dan Tŷ Mawr (SN 520 228)

The summit height produced by LIDAR analysis is 72.65m and is positioned at SN 52004 22867, 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 72.65m and this was derived from LIDAR analysis, this is 3.65m higher than the previously listed summit height of 69m, 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 and 5.65m higher than its originally listed interpolated height of c 67m.

 

The full details for the hill are:

Group:  Mynydd Mallaen 

Name:  Allt Dan Tŷ Mawr 

OS 1:50,000 map:  159

Summit Height (New Height):  72.65m (LIDAR) 

Summit Grid Reference:  SN 52004 22867 (LIDAR)               

Bwlch Height:  39.0m (LIDAR) 

Bwlch Grid Reference:  SN 52223 22857 (LIDAR) 

Drop:  33.7m (LIDAR) 

Dominance:  46.32% (LIDAR)

 

Myrddyn Phillips (May 2022)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Pen Lan Fawr (SN 626 222) - 32nd significant height revision

Hill Reclassification post for Pen Lan Fawr

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Pen Lan Fawr (SN 626 222)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m 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 Pen Lan Fawr 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 a minor road to its north, the Afon Tywi to its south and the A483 road to its east, and has the town of Llandeilo towards the north-east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a 95m summit height, based on the spot height that is positioned at SN 62616 22258 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 Pen Lan Fawr (SN 626 222)

The summit height produced by LIDAR analysis is 98.3m and is positioned at SN 62626 22229, 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 98.3m and this was derived from LIDAR analysis, this is 3.3m higher than the originally listed summit height of 95m, 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:  Pen Lan Fawr 

OS 1:50,000 map:  159

Summit Height (New Height):  98.3m (LIDAR) 

Summit Grid Reference:  SN 62626 22229 (LIDAR)               

Bwlch Height:  64.9m (LIDAR) 

Bwlch Grid Reference:  SN 61761 22561 (LIDAR) 

Drop:  33.4m (LIDAR) 

Dominance:  33.97% 

 

Myrddyn Phillips (May 2022)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Cefn Coch (SH 610 396) - 31st significant height revision

Survey post for Cefn Coch

Hill Reclassifications post for Cefn Coch

Significant Name Changes post for Cefn Coch

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Coch (SH 610 396)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m 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, with the Introduction to 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 Cefn Coch and it is adjoined to the Moelwynion group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A498 road and the B4410 road to its north-west, the A497 road and the A487 road to its south-west and the A4085 road to its east, and has the town of Penrhyndeudraeth towards the south. 

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 Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the P30 category, and it was listed with an 81m summit height, with an accompanying note stating; 86m on 1984 1:50,000 map. 

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 33m of drop and 40.74% dominance, based on the 81m summit spot height and the 48m bwlch spot height that appear 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 subsequently re-assessed as the bwlch contouring on the Ordnance Survey 1:25,000 Explorer map is between 50m – 60m, therefore according to map contouring the 48m spot height is below the position of the bwlch.  This reassessment resulted in the hill being listed with an estimated c 26m of drop, based on the 81m summit spot height and an estimated c 55m bwlch height. 

The details for this hill were later reassessed and the 86m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger map was favoured over that of the 81m spot height, and with the bwlch height amended to an estimated c 54m, these values gave this hill an estimated c 32m of drop and 37.21% dominance. 

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 Cefn Coch (SH 610 396)

The summit height produced by LIDAR analysis is 86.6m 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 86.6m and this was derived from LIDAR analysis, this is 5.6m higher than the originally listed summit height of 81m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer maps.

 

The full details for the hill are:

Group:  Moelwynion 

Name:  Cefn Coch 

OS 1:50,000 map:  124

Summit Height (New Height):  86.6m (LIDAR) 

Summit Grid Reference:  SH 61030 39620 (LIDAR)               

Bwlch Height:  51.5m (LIDAR) 

Bwlch Grid Reference:  SH 61461 39763 (LIDAR) 

Drop:  35.1m (LIDAR) 

Dominance:  40.51% (LIDAR) 

 

Myrddyn Phillips (December 2021)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Ynys Dafydd (SH 646 174) - 30th significant height revision

Hill Reclassifications post for Ynys Dafydd

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 obtained from the summit analysis programme using LIDAR produced by Joe Nuttall, and then by LIDAR analysis initially conducted by Jim Bloomer and subsequently by Myrddyn Phillips. 

LIDAR image of Ynys Dafydd (SH 646 174)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m 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, with the Introduction to 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 Ynys Dafydd, and it is adjoined to the Rhinogydd group of hills, which are situated in the western part of North Wales (Region A, Sub-Region A3), and it is positioned with the coast to its south-west, the Afon Dyfi (River Dovey) to its south and the A496 road to its north-west, and has the town of Abermaw (Barmouth) 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 Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used in the main P30 category. 

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 27m of drop based on an estimated c 42m summit height and an estimated c 15m bwlch height, with both values based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map, with 40m being the uppermost contour given the hill on this 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 Ynys Dafydd

The summit height produced by LIDAR analysis is 52.8m 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, this hill’s new listed summit height is 52.8m and this was derived from LIDAR analysis, this is 10.8m higher than the previous listed summit height of c 42m which was derived from interpolation of the uppermost contour given the hill on contemporary Ordnance Survey 1:25,000 Explorer maps.

 

The full details for the hill are:

Group:  Rhinogydd 

Name:  Ynys Dafydd 

OS 1:50,000 map:  124

Summit Height (New Height):  52.8m (LIDAR) 

Summit Grid Reference:  SN 64636 17484 (LIDAR) 

Bwlch Height:  17.1m (LIDAR) 

Bwlch Grid Reference:  SN 64599 17744 (LIDAR) 

Drop:  35.7m (LIDAR) 

Dominance:  67.61% (LIDAR)

 

Myrddyn Phillips (September 2021)

 

 

 

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Ynys Hir (SN 679 957) - 29th significant height revision

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 by Joe Nuttall who produced a summit analysis programme using LIDAR, and then by LIDAR analysis initially conducted by Chris Crocker and subsequently by Myrddyn Phillips. 

LIDAR image of Ynys Hir (SN 679 957)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m 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, with the Introduction to 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 Ynys Hir, and it is adjoined to the Pumlumon group of hills which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the Afon Dyfi (River Dovey) and the coast to its west and has the A487 road to its east and the village of Y Borth towards the south-west. 

When the original 30-99m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website this hill was included in the main P30 list with a summit height of c 40m.  

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 41m of drop, based on an estimated c 48m summit height and an estimated c 7m bwlch height, with both values based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map, with 40m being the uppermost contour given the hill on this 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 summit height produced by LIDAR analysis is 61.1m 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, this hill’s new listed summit height is 61.1m and this was derived from LIDAR analysis, this is 13.1m higher than the previous listed summit height of c 48m which was derived from interpolation of the uppermost contour given the hill on contemporary Ordnance Survey 1:25,000 Explorer maps.

 

The full details for the hill are:

Group:  Pumlumon 

Name:  Ynys Fach 

OS 1:50,000 map:  135

Summit Height (New Height):  61.1m (LIDAR) 

Summit Grid Reference:  SN 67972 95798 (LIDAR) 

Bwlch Height:  6.8m (LIDAR) 

Bwlch Grid Reference:  SN 68354 95558 & SN 68368 95541 (LIDAR) 

Drop:  54.35m (LIDAR) 

Dominance:  88.91% (LIDAR)

 

Myrddyn Phillips (August 2021)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

The Park (SN 664 936) - 28th significant height revision

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 The Park (SN 664 936)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m 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, with the Introduction to 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 The Park, and it is adjoined to the Pumlumon group of hills which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the Afon Dyfi to its north, the coast to its west and the A487 road to its east, and has the village of Tal-y-bont towards the south. 

When the original 30-99m 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 the details for this hill were re-evaluated, and it was listed with an estimated c 41m drop and 49.40% dominance, based on an estimated c 83m summit height and the 42m bwlch 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 summit image of The Park (SN 664 936)

The summit height produced by LIDAR analysis is 85.6m 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 85.6m and this was derived from LIDAR analysis, this is 2.6m higher than the previous listed summit height of c 83m which was derived from interpolation of the uppermost contour given the hill on contemporary Ordnance Survey 1:25,000 Explorer maps.

 

The full details for the hill are:

Group:  Pumlumon 

Name:  The Park 

OS 1:50,000 map:  135

Summit Height (New Height):  85.6m (LIDAR)

Summit Grid Reference:  SN 66441 93678 (LIDAR)

Bwlch Height:  42.7m (LIDAR)

Bwlch Grid Reference:  SN 66477 93308 (LIDAR)

Drop:  42.9m (LIDAR)

Dominance:  50.09% (LIDAR)

 

Myrddyn Phillips (August 2021)

 

 

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Pen y Graig Wen (SH 446 879) - 27th significant height revision

Hill Reclassifications post for Pen y Graig Wen

Summit Relocations post for Pen y Graig Wen

Significant Name Changes post for Pen y Graig Wen

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Pen y Graig Wen (SH 446 879)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Pen y Graig Wen and this was derived from the Tithe map and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the coast to its east, minor roads to its north, south and east and the B5111 road to its west, and has the village of Rhos-y-bol towards the west north-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 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-evaluated and it was listed with an estimated c 24m of drop, based on an estimated c 92m summit height positioned at SH 44769 87804 and an estimated c 68m bwlch height, with both heights 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

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 94.3m, 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, this hill’s new listed summit height is 94.3m and this was derived from LIDAR analysis, this is 2.3m higher than the previous listed summit height of c 92m which was based on interpolation of the uppermost 90m contour that appears on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Ynys Môn 

Name:  Pen y Graig Wen 

OS 1:50,000 map:  114

Summit Height (New Height):  94.3m (LIDAR) 

Summit Grid Reference:  SH 44637 87986 (LIDAR) 

Bwlch Height:  68.2m (LIDAR) 

Bwlch Grid Reference:  SH 45162 88579 (LIDAR) 

Drop:  26.1m (LIDAR) 

 

Myrddyn Phillips (July 2021)

 

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Ynys Cynfelyn (SN 649 919) - 26th significant height revision

Significant Name Changes post for Ynys Cynfelyn

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Ynys Cynfelyn (SH 649 919)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m 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, with the Introduction to 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 Ynys Cynfelyn, and it is adjoined to the Pumlumon group of hills which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the coast to its west, the B4353 road to its north, a minor road to its south and the A487 road to its east, and has the village of Tal-y-bont towards the south. 

When the original 30-99m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website this hill was included in the main P30 list with a c 40m summit height. 

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 listed with an estimated c 36m of drop based on an estimated c 43m summit height and an estimated c 7m bwlch height, with both values 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 Ynys Cynfelyn (SH 649 919)

The summit height produced by LIDAR analysis is 45.1m 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 45.1m and this was derived from LIDAR analysis, this is 2.1m higher than the previous listed summit height of c 43m which was derived from interpolation of the uppermost contour given the hill on contemporary Ordnance Survey 1:25,000 Explorer maps.

 

The full details for the hill are:

Group:  Pumlumon 

Name:  Ynys Cynfelyn 

OS 1:50,000 map:  135

Summit Height (New Height):  45.1m (LIDAR) 

Summit Grid Reference:  SN 64923 91967 (LIDAR) 

Bwlch Height:  5.5m (LIDAR) 

Bwlch Grid Reference:  SN 65441 92012 (LIDAR) 

Drop:  39.65m (LIDAR) 

Dominance:  87.88% (LIDAR) 

 

Myrddyn Phillips (July 2021)

 

 

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Penymorwydd (SH 384 912) - 25th significant height revision

Hill Reclassifications post for Penymorwydd

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Penymorwydd (SH 384 912)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Penymorwydd and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is encircled by minor roads with the A5025 road farther to its north-west, and has the village of Cemaes towards the north-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 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-evaluated and it was listed with an estimated c 26m of drop based on the 69m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 43m bwlch height based on interpolation of 5m contouring between 40m – 45m. 

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 Penymorwydd

The summit height produced by LIDAR analysis is 70.5m, 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, this hill’s new listed summit height is 70.5m and this was derived from LIDAR analysis, this is 1.5m higher than the previous listed summit height of 69m 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:  Ynys Môn 

Name:  Penymorwydd 

OS 1:50,000 map:  114

Summit Height (New Height):  70.5m (LIDAR) 

Summit Grid Reference:  SH 38471 91255 (LIDAR) 

Bwlch Height:  c 43m (interpolation) 

Bwlch Grid Reference:  SH 38636 90826 (interpolation) 

Drop:  c 28m (LIDAR summit and interpolated bwlch) 

 

Myrddyn Phillips (July 2021)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Tyddyn Gwydryn Llain Fan (SH 495 681) - 24th significant height revision

Hill Reclassifications post for Tyddyn Gwydryn Llain Fan

Summit Relocations post for Tyddyn Gwydryn Llain Fan

Significant Name Changes post for Tyddyn Gwydryn Llain Fan

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Tyddyn Gwydryn Llain Fan (SH 495 681)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Tyddyn Gwydryn Llain Fan and this was derived from the Tithe map, and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with its summit adjacent to the A4080 road, and has the village of Brynsiencyn towards the 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 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-evaluated and it was listed with an estimated c 26m of drop based on the 59m spot height adjoined to a triangulation pillar positioned at SH 49980 68424 and the 59m spot height positioned at SH 50109 68526 and an estimated c 33m bwlch height based on interpolation of 5m contouring between 30m – 35m that appear 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 summit height produced by LIDAR analysis is 60.4m, 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, this hill’s new listed summit height is 60.4m and this was derived from LIDAR analysis, this is 1.4m higher than the previous listed summit height of 59m which was based on the spot height adjoined to a triangulation pillar positioned at SH 49980 68424 and the spot height positioned at SH 50109 68526 that appear on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Ynys Môn 

Name:  Tyddyn Gwydryn Llain Fan 

OS 1:50,000 map:  114, 115

Summit Height (New Height):  60.4m (LIDAR) 

Summit Grid Reference:  SH 49584 68102 (LIDAR) 

Bwlch Height:  31.9m (LIDAR) 

Bwlch Grid Reference:  SH 51324 71408 (LIDAR) 

Drop:  28.5m (LIDAR) 

 

Myrddyn Phillips (May 2021)

 

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Menai Rock (SH 555 716) - 23rd significant height revision

Hill Reclassifications post for Menai Rock

Significant Name Changes post for Menai Rock

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Menai Rock (SH 555 716)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Menai Rock and this was derived from the Tithe map, and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A545 road to its immediate north-west and the A5 road to its south, and has the town of Porthaethwy (Menai Bridge) surrounding it. 

When the original 30-99m 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-evaluated and it was listed with an estimated c 19m of drop based on the 31m 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 12m bwlch height based on interpolation of 5m contouring between 10m – 15m that appear 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 summit height produced by LIDAR analysis is 33.1m, 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. 

LIDAR summit image of Menai Rock

Therefore, this hill’s new listed summit height is 33.1m and this was derived from LIDAR analysis, this is 2.1m higher than the previous listed summit height of 31m 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:  Ynys Môn 

Name:  Menai Rock 

OS 1:50,000 map:  114, 115

Summit Height (New Height):  33.1m (LIDAR) 

Summit Grid Reference:  SH 55569 71697 (LIDAR) 

Bwlch Height:  9.0m (LIDAR) 

Bwlch Grid Reference:  SH 55622 72078 (LIDAR) 

Drop:  24.1m (LIDAR) 

 

Myrddyn Phillips (April 2021)

 

  

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Castell (SN 585 789) - 22nd significant height revision

Survey post for Castell

Hill Reclassifications post for Castell

Significant Name Changes post for Castell

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 derived from LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

The view from the summit of Castell (SN 585 789)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m 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, with the Introduction to 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 Castell and it is adjoined to the Elenydd group of hills which are situated in the central part of the Mid and West Wales Region (Region B, Sub-Region B2), and it is positioned with the coast to its west, the Afon Ystwyth to its east and the A487 road farther to its east, and has the town of Aberystwyth towards the north. 

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 Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for the main P30 category. 

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 29m of drop, based on the 73m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 44m bwlch height based on interpolation of 10m contouring between 40m – 50m. 

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

The details for this hill we re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and for this hill a 41m spot height appeared on the area of its bwlch and when coupled with the 73m summit spot height these values give this hill 32m of drop. 

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 Castell

The summit height produced by LIDAR analysis is 77.4m, and as the summit has now been surveyed with the Trimble GeoXH 6000 giving 77.2m it is this result that is being prioritised for listing purposes, 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, this hill’s new listed summit height is 77.2m and this was derived from a Trimble GeoXH 6000 survey, this is 4.2m higher than the previous listed summit height of 73m which was based on the spot height that appears on contemporary Ordnance Survey 1:25,000 Explorer maps.

 

The full details for the hill are:

Group:  Elenydd 

Name:  Castell 

OS 1:50,000 map:  135

Summit Height (New Height):  77.2m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SN 58516 78997 (Trimble GeoXH 6000) 

Bwlch Height:  42.3m (LIDAR) 

Bwlch Grid Reference:  SN 58197 78954 (LIDAR) 

Drop:  34.9m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Dominance:  45.21% (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (April 2021)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Ynys Fach (SN 668 951) - 21st significant height revision

Hill Reclassifications post for Ynys Fach

Summit Relocations post for Ynys Fach

Significant Name Changes post for Ynys Fach

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 by Joe Nuttall who produced a summit analysis programme using LIDAR, and then by LIDAR analysis initially conducted by Jim Bloomer and subsequently by Myrddyn Phillips. 

LIDAR image of Ynys Fach (SN 668 951)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m 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, with the Introduction to 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 Ynys Fach, and it is adjoined to the Pumlumon group of hills which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it has the A487 road to its south-east and the town of Machynlleth towards the north-east. 

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 Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used in the main P30 category. 

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 listed with an estimated c 27m of drop based on an estimated c 34m summit height and an estimated c 7m bwlch height, with both values based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map, with 30m being the uppermost contour given the hill on this 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 Ynys Fach

The summit height produced by LIDAR analysis is 43.5m 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, this hill’s new listed summit height is 43.5m and this was derived from LIDAR analysis, this is 9.5m higher than the previous listed summit height of c 34m which was derived from interpolation of the uppermost contour given the hill on contemporary Ordnance Survey 1:25,000 Explorer maps.

 

The full details for the hill are:

Group:  Pumlumon 

Name:  Ynys Fach 

OS 1:50,000 map:  135

Summit Height (New Height):  43.5m (LIDAR) 

Summit Grid Reference:  SN 66845 95141 (LIDAR) 

Bwlch Height:  2.1m (LIDAR) 

Bwlch Grid Reference:  SN 67483 95096 (LIDAR) 

Drop:  41.3m (LIDAR) 

Dominance:  95.10% (LIDAR)

 

Myrddyn Phillips (April 2021)

 

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

The Larches (ST 433 899) - 20th significant height revision

Significant Name Changes post for The Larches

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Larches (ST 433 899)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m 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, with the Introduction to 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 The Larches, 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 minor roads to its north, west, south and east and further afield has the A48 road to its north and the M4 motorway to its south, and has the city of Casnewydd (Newport) towards the west.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a c 85m summit height, this being the uppermost contour that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at ST 433 899.

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

When this list was standardised, and interpolated heights and drop values also included the details for this hill was re-assessed and it was listed with an estimated c 89m summit height based on interpolation of 5m contouring 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 summit image of The Larches

The summit height produced by LIDAR analysis is 91.1m 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, this hill’s new listed summit height is 91.1m and this was derived from LIDAR analysis, this is 2.1m higher than the previous listed summit height of c 89m and 6.1m higher than the uppermost 85m ring contour on contemporary Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Group:  Gwent Is Coed

Name:  The Larches

OS 1:50,000 map:  171, 172

Summit Height (New Height):  91.1m (LIDAR)

Summit Grid Reference:  ST 43303 89957 (LIDAR)

Bwlch Height:  22.3m (LIDAR)

Bwlch Grid Reference:  ST 42928 90248 (LIDAR)

Drop:  68.8m (LIDAR)

Dominance:  75.54% (LIDAR)

Myrddyn Phillips (September 2020)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Waltwood Hill (ST 386 885) - 19th significant height revision

Summit Relocations post for Waltwood Hill

There has been a Significant Height Revision to a hill that is listed in the 30-99m 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 Waltwood Hill (ST 386 885)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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, with the Introduction to 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 Waltwood 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 M4 motorway to its north, the A48 road to its west and the A4810 road to its south, and has the city of Casnewydd (Newport) towards the west.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 68m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at ST 38637 88605.

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 Waltwood Hill

The summit height produced by LIDAR analysis is 70.2m 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, this hill’s new listed summit height is 70.2m and this was derived from LIDAR analysis, this is 2.2m higher than the previous listed summit height of 68m that appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Gwent Is Coed

Name:  Waltwood Hill

OS 1:50,000 map:  171

Summit Height (New Height):  70.2m (LIDAR)

Summit Grid Reference:  ST 38646 88595 (LIDAR)

Bwlch Height:  21.7m (LIDAR)

Bwlch Grid Reference:  ST 39426 89069 and ST 39433 89070 (LIDAR)

Drop:  48.5m (LIDAR)

Dominance:  69.07% (LIDAR)

Myrddyn Phillips (August 2020)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Dinas Powys (ST 148 722) - 18th significant height revision

Hill Reclassifications post for Dinas Powys

There has been a Significant Height Revision to a hill that is now listed in the 30-99m 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 Dinas Powys (ST 148 722)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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, with the Introduction to the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name the hill is listed by is Dinas Powys 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 encircled by a number of A roads, with the A4232 to its north, the A4050 to its west, the A4231 towards its south and the A4055 to its east, and has the town of Y Barri (Barry) to the south-west and the town of Penarth towards the east.

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 Hills to be surveyed sub list that accompanied the main P30 list, as it did not meet the criteria then used in the main P30 list. 

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 29m of drop based on a c 62m interpolated summit height and the 33m spot height that appears at the bwlch on Ordnance Survey 1:25,000 Explorer maps which for this area has contours at 5m intervals.

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

The details for this hill were re-examined 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 has many spot heights not on other publicly available Ordnance Survey maps.

Extract from the Ordnance Survey Vector Map Local

The details for this hill were also re-assessed when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and the online Vector Map Local.  These re-assessments resulted in the hill being listed with c 30m of drop with the interpolated summit height increasing from c 62m to c 63m.

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 Dinas Powis

The summit height produced by LIDAR analysis is 69.4m 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, this hill’s new listed summit height is 69.4m and this was derived from LIDAR analysis, this is 6.4m higher than the previous estimated summit height of c 63m and 9.4m higher than the uppermost 60m ring contour on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, but it is in accordance with the uppermost 65m ring contour on the OS Maps website.

The full details for the hill are:

Group:  Bro Morgannwg

Name:  Dinas Powys

OS 1:50,000 map:  171

Summit Height (New Height):  69.4m (LIDAR)

Summit Grid Reference:  ST 14823 72225 (LIDAR)

Bwlch Height:  33.6m (LIDAR)

Bwlch Grid Reference:  ST 14757 72333 (LIDAR)

Drop:  35.8m (LIDAR)

Dominance:  51.57% (LIDAR)

Myrddyn Phillips (November 2019)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Ash Tip (ST 031 663) - 17th significant height revision

Hill Reclassifications post for Ash Tip

Significant Name Changes post for Ash Tip

There has been a Significant Height Revision to a hill that is now listed in the 30-99m 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 Ash Tip (ST 031 663)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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, with the Introduction to the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name the hill is now listed by is Ash Tip and this was derived from local enquiry, 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 forms a part of landscaped ground that once made up the Aberthaw quarry and lime works, and it is positioned with the B4265 road to its north, and has the small community of Sain Tathan (St Athan) towards the north-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 not included in either the main P30 list or the Hills to be surveyed sub list, as contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps of the day showed the area that now makes up this hill as having no 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.

The summit height produced by LIDAR analysis is 50.0m and as there are no contours of any significance on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, 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, this hill’s new listed summit height is 50.0m and this was derived from LIDAR analysis, this is 40m higher than the uppermost 10m ring contour on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Group:  Bro Morgannwg

Name:  Ash Tip

OS 1:50,000 map:  170

Summit Height (New Height):  50.0m (LIDAR)

Summit Grid Reference:  ST 03170 66338 (LIDAR)

Bwlch Height:  12.4m (LIDAR)

Bwlch Grid Reference:  ST 03298 66735 (LIDAR)

Drop:  37.6m (LIDAR)

Dominance:  75.20% (LIDAR)

Myrddyn Phillips (November 2019)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Pt. 22.2m (SM 701 226) - 16th significant height revision

Hill Reclassifications post for Pt. 22.2m

There has been a Significant Height Revision to a hill that is now listed in the 30-99m Twmpau and Y Pellennig – The Remotest 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 Aled Williams.

Pt. 22.2m (SM 701 226)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category which this hill is a part of is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m 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.  This list is authored by Myrddyn Phillips.

Y Pellennig – The Remotest Hills of Wales - Welsh hills whose summit is at least 2.5km from the nearest paved public road and the hill has a minimum 15m of drop, the list is a joint compilation between Myrddyn Phillips and Aled Williams and is available as a downloadable e-booklet or print-booklet version on Mapping Mountains Publications with the up-to-date master list available on the Mapping Mountains site in Google Doc format.

As the authors do not know an appropriate name for this hill either from historic research or local enquiry it is being listed by the point (Pt. 22.2m) notation, and it is adjoined to the Carn Llidi group of hills which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4), and it is positioned in a small sheltered bay on the southern side of Ynys Dewi.

This hill did not appear in the accompanying Hills to be surveyed sub list when the original Welsh 30-99m P30 hills were published on Geoff Crowder’s v-g.me website, as it did not meet the criteria then used for this sub category, however this sub list has now been standardised, with interpolated drop values and interpolated summit heights also included.

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

Even when this sub list was standardised contemporary Ordnance Survey 1:25,000 Explorer maps do not give the hill any contour ring.  The lack of contour rings is also applicable to the Ordnance Survey Vector Map Local hosted on the Geograph website which is entitled the Interactive Coverage Map.

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

The details for this hill were re-assessed when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has 5m contour intervals, and this mapping gives this hill an uppermost 15m ring contour.

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.

The summit height produced by LIDAR analysis is 22.2m, this height comes within the parameters of the Significant Height Revisions used within this page heading, and 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.

LIDAR image of Pt. 22.2m, 1m contour (black), 10m contour (red) and sea level (yellow)

Close up LIDAR image of Pt. 22.2m, 1m contour (black), 10m contour (red) and sea level (yellow)

Therefore, this hill’s new listed summit height is 22.2m and this was derived from LIDAR analysis conducted by Aled Williams, this is 22.2m higher than information on the Ordnance Survey 1:25,000 Explorer map and 7.2m higher than the uppermost 15m contour ring on the OS Maps website.

The full details for the hill are:

Group:  Carn Llidi 

Name:  Pt. 22.2m

OS 1:50,000 map:  157

Summit Height (New height):  22.2m (LIDAR)

Summit Grid Reference:  SM 70180 22696 (LIDAR)

Bwlch Height:  N/A, sea level

Bwlch Grid Reference:  N/A, sea level

Drop:  22.2m (LIDAR)

Remoteness:  3.400km

Myrddyn Phillips (June 2019)

© Crown: CHERISH PROJECT 2019. Produced with EU funds through the Ireland Wales Co-operation Programme 2014-2020. All material made freely available through the Open Government Licence.

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Mynydd Bach (SH 389 767) - 15th significant height change

Survey post for Mynydd Bach

Significant Name Changes post for Mynydd Bach

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height confirmed by LIDAR analysis, and a subsequent survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter taking place on the 28^th October 2018.

LIDAR summit image of Mynydd Bach

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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, with the Introduction to the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name of the hill is Mynydd Bach and this was derived from local enquiry and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it has the A5 and A55 roads and the village of Gwalchmai towards its south.

When the original 30—99m 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 95m, when this list was standardised with interpolated heights and drop values also included the hill was listed with an estimated c 97m summit height based on its uppermost 95m ring contour 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 next 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 map has a 99m spot height in the vicinity of this hill’s summit, however this spot height is placed on a covered reservoir, and as this is considered a recent man-made construct it is not taken as a part of the hill’s overall height.

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 is in good accordance with that produced by the Trimble GeoXH 6000 survey, and even though the spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website is placed on the top of a covered reservoir, 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.  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 96.5m and this was derived from the Trimble GeoXH 6000 survey, this is 2.5m lower than the 99m 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:  Ynys Môn 

Name:  Mynydd Bach

OS 1:50,000 map:  114

Summit Height (New height):  96.5m (converted to OSGM15)

Summit Grid Reference:  SH 38964 76773

Bwlch Height:  c 64m

Bwlch Grid Reference:  SH 40259 77918 (I)

Drop:  c 32m

Dominance:  33.66%

For details on the summit survey of this hill

Myrddyn Phillips (May 2019)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Coed Darcy (SS 711 955) - 14th significant height revision

Hill Reclassifications post for Coed Darcy

Significant Name Changes post for Coed Darcy

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and was listed in the Y Trechol – The Dominant Hills of Wales, with the summit height, its location, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Coed Darcy (SS 711 955)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 30m of drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 Coed Darcy and it is adjoined to the Fforest Fawr group of hills, which are situated in the northern part of South Wales (Region C, Sub-Region C2), and it is positioned with the B4290 and M4 roads to its east, and has the town of Castell-neth (Neath) towards the north-east.

When the original 30—99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill appeared in the accompanying Hills to be surveyed sub list as it did not meet the criteria then used for the main P30 list; however this sub list has now been standardised with drop values and interpolated heights also included in the main P30 and the accompanying sub list.

After this list was standardised and interpolated heights also included this hill was listed with 31m of drop and 37.35% of dominance, based on the 83m summit spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map and a bwlch height of 52m based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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 were next 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 80.4m and is positioned at SS 71147 95565, and the bwlch height is 53.0m and is positioned at SS 71330 95324, with these values giving this hill 27.4m of drop 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.  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 summit height is 80.4m and this was produced from LIDAR analysis, this is 2.6m lower than its previously listed height of 83m which appears as a spot height 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:  Fforest Fawr

Name:  Coed Darcy

OS 1:50,000 map:  170

Summit Height (New height):  80.4m (LIDAR)

Summit Grid Reference:  SS 71147 95565 (LIDAR)

Bwlch Height:  53.0m (LIDAR)

Bwlch Grid Reference:  SS 71330 95324 (LIDAR)

Drop:  27.4m (LIDAR)

Dominance:  N/A, insufficient drop (LIDAR)

Myrddyn Phillips (May 2019)






Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Broughton Burrows (SS 413 927) - 13th significant height revision

Summit Relocations post for Broughton Burrows

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the hill’s height, drop and dominance confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Broughton Burrows

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 30m of drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 addition Welsh P30 hills whose prominence is 33.33% or more and below 50% 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 Broughton Burrows, and it is adjoined to the Gŵyr group of hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and it is positioned at the western end of the Gŵyr, and has the small community of Llangynydd towards the south-east.

Although the summit of this hill is not a part of open access land, and as such permission to visit should be sought, there is general acceptance for people to visit, with the nearest public footpath encircling the summit of the hill which comprises a dune system.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 49m summit height which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

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

When interpolated height and also drop values were added to these lists, this hill was listed with c 32m of drop based on the 49m spot height and an interpolated bwlch height of c 17m based on what was thought to be bwlch contouring between 15m – 20m as indicated on the 1:25,000 Explorer map.  However, as this hill is a part of a dune system this map did not show continuous contours on either the summit or bwlch area of this hill.

Prior to LIDAR analysis this hill was analysed using the 5m contouring on OS Maps, which is the recent replacement for OS Get-a-map.  The bwlch height was confirmed as being between 15m – 20m and an interpolated height of c 18m the listed.  However, this mapping showed a number of 60m continuous ring contours for the summit area of this hill and therefore LIDAR was examined, with the summit height produced being 61.9m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Extract from OS Maps

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 summit height is 61.9m and this was produced from LIDAR analysis, this is 12.9m higher than its previously listed height of 49m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map, however this new height is in accordance with the 5m contouring on OS Maps.

LIDAR summit image of Broughton Burrows

Close up LIDAR summit image of Broughton Burrows

The full details for the hill are:

Group:  Gŵyr

Name:  Broughton Burrows

OS 1:50,000 map:  159

Summit Height (New height):  61.9m (LIDAR)

Summit Grid Reference:  SS 41391 92781 (LIDAR)

Bwlch Height:  17.4m (LIDAR)

Bwlch Grid Reference:  SS 41739 92663 (LIDAR) 

Drop:  44.5m (LIDAR)

Dominance:  71.95% (LIDAR)

Myrddyn Phillips (December 2018)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Burry Holms (SS 398 926) - 12th significant height revision

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the hill’s height, drop, dominance and status confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR summit image of Burry Holms

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 30m of drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 addition Welsh P30 hills whose prominence is 33.33% or more and below 50% 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 Burry Holms, and as this name implies the hill is a part of an island, and it is adjoined to the Gŵyr group of hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and is positioned at the western end of the Gŵyr, with the small community of Llangynydd towards the east south-east.

Although the island is not a part of open access land, and as such permission to visit should be sought, there is general acceptance for people to visit, with the nearest public footpath leading to the beach and island to the east on the western part of Broughton Burrows.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 35m summit height based on information from David Purchase who had noted a 35m spot height on the Ordnance Survey 1:10,000 map.

Prior to LIDAR analysis the uppermost 30m ring contour on contemporary Ordnance Survey maps had been interpolated, giving an estimated summit height of c 33m.  However, even though the 1:10,000 mapping is prioritised over this interpolated summit height, the 35.1m height produced by LIDAR analysis still comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

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 summit height is 35.1m and this was produced from LIDAR analysis, this height is only 0.1m higher than the previously listed height of 35m which was derived from the Ordnance Survey 1:10,000 map, but it is 2.1m higher than the interpolated height of c 33m taken from contemporary Ordnance Survey maps.

LIDAR bwlch image of Burry Holms

The full details for the hill are:

Group:  Gŵyr

Name:  Burry Holms

OS 1:50,000 map:  159

Summit Height (New height):  35.1m (LIDAR)

Summit Grid Reference:  SS 39863 92603 (LIDAR)

Bwlch Height:  0.3m (LIDAR)

Bwlch Grid Reference:  SS 40173 92525 (LIDAR) 

Drop:  34.8m (LIDAR)

Dominance:  99.02% (LIDAR)

Myrddyn Phillips (December 2018)






Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Ynys Deullyn (SM 844 340) - 11th significant height revision

Hill Reclassifications post for Ynys Deullyn

There has been a Significant Height Revision to a hill that appears in the following lists; 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the hill’s height, drop, dominance and status confirmed by LIDAR analysis conducted by Myrddyn Phillips.

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 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.

The name of the hill is Ynys Deullyn and as its name implies it is an island, or more strictly speaking a tidal island that is attached to mainland Wales at low tide.  The hill is adjoined to the Carn Llidi group of hills, which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4), with the island being positioned on the northern part of the Pembrokeshire coast, and it has the small community of Abercastell towards its west south-west.

If wanting to visit the island permission to do so should be sought as it is not a part of designated open access land, for those wishing to do so caution is advised as the easiest approach will probably necessitate some form of scramble.

This hill did not appear in the main P30 list or the accompanying Hills to be surveyed sub list when the original Welsh P30 hills were published on Geoff Crowder’s v-g.me website, as it was thought not to have 30m of drop and did not meet the criteria then used for the sub category; however this sub list has now been standardised including the addition of interpolated drop and height values.

This hill was included as a P30 shortly after the Ordnance Survey Interactive Coverage Map became available on the Geograph website, and prior to LIDAR analysis it was listed with 30m of drop based on the 30m summit spot height that appears on this map.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

The summit height produced by 2m DSM LIDAR analysis is 32.6m, this is not a dramatic height revision when 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:

2m DSM LIDAR image of Ynys Deullyn (SM 844 340)

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 by LIDAR analysis, 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 summit height is 32.6m and this was produced from LIDAR analysis, this is 2.6m higher than its previously listed height of 30m which appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

The full details for the hill are:

Group:  Carn Llidi

Summit Height (New Height):  32.6m (LIDAR)

Name:  Ynys Deullyn

OS 1:50,000 map:  157

Summit Grid Reference:  SM 84479 34095 (LIDAR) 

  

Drop:  30.5m (LIDAR)

Dominance:  93.51% (LIDAR) 

Myrddyn Phillips (September 2018)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Fegla Fach (SH 638 153) - 10th significant height revision

Survey post for Fegla Fach

Hill Reclassifications post for Fegla Fach

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, drop, dominance and status of the hill confirmed by a combination of LIDAR analysis and a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 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.

The name of the hill is Fegla Fach and it is adjoined to the Cadair Idris group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), with the hill being positioned between the Afon Mawddach to its north-west and the A 493 road to its south-east, and has the village of Y Friog (Fairbourne) to the south-west.  

As the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so access to its summit can be found from the confines of a camp site which is situated at the base of the hill to its south-west.

Prior to LIDAR analysis and the Trimble survey this hill was listed with 25m of drop based on the 28m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 3m bwlch spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

The summit height produced by LIDAR analysis is 31.5m, this is not a dramatic height revision when 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:

LIDAR image of Fegla Fach (top right of photograph) and showing the Arthog bog

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 summit height is 31.5 and this was produced by LIDAR analysis, this is 3.5m higher than its previously listed height of 28m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Cadair Idris

Summit Height (New Height):  31.5m (LIDAR)

Name:  Fegla Fach

OS 1:50,000 map:  124

Summit Grid Reference:  SH 63818 15311 (LIDAR)   

Drop:  30.0m (LIDAR summit and Trimble bwlch)

Dominance:  95.37% (LIDAR summit and Trimble bwlch)

The summit of Fegla Fach (SH 638 153)

For details on the survey and on-site visit that significantly revised the summit height of this hill

Myrddyn Phillips (August 2018)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Fegla Fawr (SH 629 146) - 9th significant height revision

Survey post for Fegla Fawr

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, drop and dominance of the hill confirmed by a Trimble GeoXH 6000 survey and LIDAR analysis conducted by Myrddyn Phillips.

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 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.

The name of the hill is Fegla Fawr and it is adjoined to the Cadair Idris group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), with the hill being positioned between the Afon Mawddach to its north-west and north and the A 493 road to its south-east, and has the village of Y Friog (Fairbourne) to the south-west.  

As the hill is not a part of designated open access land permission to visit should be sought, however there are paths leading toward its summit which is an indicator that local concession exists to visit it summit.

Prior to LIDAR analysis and the Trimble survey this hill was listed with c 55m of drop based on an estimated c 57m summit height with the hill having an uppermost 50m ring contour on contemporary Ordnance Survey maps, and a bwlch height of 2m based on the spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

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

LIDAR image of Fegla Fawr

The summit height produced by the Trimble GeoXH 6000 survey is 59.5m (converted to OSGM15), this is not a dramatic height revision when 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 summit height is 59.5m (converted to OSGM15) and this was produced by the Trimble GeoXH 6000 survey, this is 2.5m higher than its previously listed height of c 57m which was estimated from the uppermost 50m ring contour on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group:  Cadair Idris

Summit Height (New Height):  59.5m (converted to OSGM15)

Name:  Fegla Fawr

OS 1:50,000 map:  124

Summit Grid Reference:  SH 62966 14665  

Drop:  57.6m (Trimble summit and LIDAR bwlch)

Dominance:  96.81% (Trimble summit and LIDAR bwlch)

Gathering data at the summit of Fegla Fawr (SH 629 146) 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 (August 2018)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Allt Fawr (SH 383 356) - 8th significant height revision

Hill Reclassifications post for Allt Fawr

Summit Relocations post for Allt Fawr

There has been a Significant Height Revision to a hill that now appears in the 30-99m Twmpau, with the summit height, drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

The criteria for this list are:

30-99m Twmpau – Welsh hills at and above 30m and below 100m in height that have a minimum 30m of drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at and above 30m and below 100m in height with 20m and 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 Allt Fawr and it is adjoined to the Pen Llŷn range of hills, which is situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A 499 road to its west and the A 497 road to its east, and has the town of Pwllheli towards its south-west.

As the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so the proximity of the roads will give relatively easy access.

Prior to LIDAR analysis this hill was listed with c 18m of drop based on an estimated c 46m summit height with the hill given three uppermost 45m ring contours on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website and an estimated bwlch height of c 28m based on bwlch contouring at 5m intervals and between 25m – 30m on this same map.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

The summit height produced by LIDAR analysis is 48.9m, this is not a dramatic height revision when 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:

LIDAR image of Allt Fawr

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 summit height is 48.9m and this was produced by LIDAR analysis, this is 2.9m higher than its previously listed height of c 46m which was estimated from the Ordnance Survey Interactive Coverage map hosted on the Geograph website.

The full details for the hill are:

Group:  Pen Llŷn

Summit Height (New Height):  48.9m (LIDAR)

Name:  Allt Fawr

OS 1:50,000 map:  123

Summit Grid Reference:  SH 38347 35695 (LIDAR)

 

Drop:  23.1m (LIDAR)

Myrddyn Phillips (April 2018)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Bryn y Bont (SH 596 459) - 7th significant height revision

Hill Relassifications post for Bryn y Bont

Summit Relocations post for Bryn y Bont

There has been a Significant Height Revision to a hill that now appears in the Double Sub-Twmpau list that accompanies the 30-99m Twmpau list, with the hill’s height and drop confirmed by analysis by Aled Williams of data produced by LIDAR.  With the title of Twmpau being an acronym for thirty welsh metre prominences and upward.

Accompanying each 100m height band within the main Twmpau list is a sub list entitled the Sub-Twmpau, with the Double Sub-Twmpau attached to the lower tier height band of Welsh hills.

The criteria for the lower tier of Twmpau hills are:

30-99m Twmpau – All Welsh hills at and above 30m and below 100m in height with 30m minimum drop.

30-99m Sub-Twmpau – All Welsh hills at and above 30m and below 100m in height with 20m or more and below 30m of drop.

Double Sub-Twmpau – All Welsh hills at and above 20m and below 30m in height with 20m or more and below 30m of drop.

The name of the hill is Bryn y Bont and it is situated in the Moelwynion range of hills and is placed in the Region of North Wales (Region A, Sub-Region A1).  The hill is positioned with the A 4085 road to its north and its east and the A 498 road to its west, and has the Afon Glaslyn also to its immediate west, with the hamlet of Nantmor positioned to the east of the hill and the village of Beddgelert towards its north.

As the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so an ascent from the convenience of the road to its north or east is likely to be the easiest.

Prior to analysis of data produced via LIDAR this hill was not listed in the Hills to be surveyed sub list that accompanied the Welsh P30 lists published on Geoff Crowder’s v-g.me website.  When these lists were re-evaluated after they were standardised and also drop values added, this hill was listed with c 16m of drop based on an estimated c 20m summit height which was based on this hill’s small uppermost 20m ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and an estimated bwlch height of c 4m based on bwlch contouring at 10m intervals and between 0 – 10m, with the caveat that the 4m spot height positioned at SH 59756 45814 and shown on the Ordnance Survey 1:25,000 Explorer map is probably not at the position of the critical bwlch.  However, since these lists were re-evaluated OS Maps (the recent replacement for OS Get-a-map) are now available and show 5m contour intervals with an uppermost 25m ring contour for this hill. 

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

Extract from the OS Maps website

The summit height produced by data via LIDAR is 25.2m, this is a dramatic height revision in relation to its previously estimated height of c 20m, and therefore 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 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, and also hill’s that do not possess a summit spot height and whose estimated summit height has a 2m or more discrepancy when compared to data produced either by the Trimble or by LIDAR.  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 summit height is 25.2m and this was produced from data via LIDAR, this is 5.2m higher than its previously listed estimated height of c 20m which was based on the small uppermost 20m ring contour on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Moelwynion

Summit Height (New Height):  25.2m (data via LIDAR)

Name:  Bryn y Bont

OS 1:50,000 map:  115

Summit Grid Reference:  SH 59641 45973

   

Drop:  20.9m (data via LIDAR)

My thanks to Aled Williams for sending the details of this hill to me

Myrddyn Phillips (February 2018)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Bryn y Gwynt (SH 599 449) - 6th significant height revision

Hill Reclassifications post for Bryn y Gwynt

Significant Name Changes post for Bryn y Gwynt

Summit Relocations post for Bryn y Gwynt

There has been a Significant Height Revision to a hill that is now listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height, their locations, the drop, dominance and status of the hill confirmed by LIDAR analysis conducted by Aled Williams and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams.

LIDAR image of Bryn y Gwynt (SH 599 449)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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, with the Introduction to 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 Bryn y Gwynt and this was derived from local enquiry and the series of Ordnance Survey Six-Inch maps and it is situated in the Moelwynion range of hills in the Region of North Wales (Region A, Sub-Region A1), and is positioned with the A 4085 road to its north-east and has the Welsh Highland Railway to its immediate west and overlooks the Afon Glaslyn also to its west, and has the village of Beddgelert to its north north-west and the town of Porthmadog to its south south-west.

The hill is a part of Coed Hafod y Llyn, and as this name implies its summit is placed in woodland which is deciduous, and as the summit is not a part of designated open access land permission to visit should be sought, however paths are indicated on the map to the north, east and south of this hill’s summit and therefore gaining access to its lower slopes has probably been accepted for many years.

Prior to LIDAR analysis this hill was listed in the Hills to be surveyed sub list that accompanied the Welsh P30 lists published on Geoff Crowder’s v-g.me website.  When these sub lists were standardised and also drop values added, this hill was listed with an estimated c 29m of drop based on the 56m spot height that appears on the Ordnance Survey 1:25,000 Explorer map at SH 59881 44828 and an estimated bwlch height of c 27m based on contouring at 10m intervals between 20m – 30m, with the caveat that the 27m spot height that appears on a road at SH 60168 45293 on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website is judged not to be positioned at the critical bwlch.

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

The summit height produced by LIDAR analysis is 58.4m and is positioned at SH 59949 44915, but as the summit has now been surveyed with the Trimble GeoXH 6000 giving 59.9m positioned at SH 59949 44919, it is this result that is being prioritised for listing purposes.  This is not a dramatic height revision when 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 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.  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.

The Trimble GeoXH 6000 gathering data at the summit of Bryn y Gwynt

Therefore, the new listed summit height of this hill is 59.9m and this was derived from a Trimble GeoXH 6000 survey, this is 3.9m higher than its previously listed height of 56m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Moelwynion

Name:  Bryn y Gwynt

OS 1:50,000 map:  124

Summit Height (New Height):  59.9m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 59949 44919 (Trimble GeoXH 6000) 

  

Bwlch Height:  28.0m (LIDAR)

Bwlch Grid Reference:  SH 60224 45248 & SH 60226 45258 & SH 60227 45259 (LIDAR)

Drop:  31.9m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  53.21% (Trimble GeoXH 6000 summit and LIDAR bwlch)  

My thanks to Aled Williams for sending the details of this hill to me.

Myrddyn Phillips (February 2018)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Bryn Tŵr (SH 604 441) - 5th significant height revision

Survey post for Bryn Tŵr

Summit Relocation post for Bryn Tŵr

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000 which took place on the 23^rd December 2017 in wet conditions but with clear visibility.

The criteria for the two lists this height revision affects are:

30-99m Twmpau – Welsh hills at and above 30m and below 100m in height that have 30m minimum drop.  With the word Twmpau being an acronym standing for ‘thirty welsh metre prominences and upward’.

Y Trechol – The Dominant Hills of Wales - Welsh P30s whose prominence equal or exceed half that of their absolute height.

The name of the hill is Bryn Tŵr and it is placed in the Moelwynion range of hills which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and the hill is positioned overlooking the A 4085 road and the Nanmor to its east, with it being positioned between the village of Beddgelert to its north north-west and Porthmadog to its south south-west. 

As the summit of the hill is not on designated open access land permission to visit should be sought, however the hill has a well-used path leading to its summit indicating that people have visited this hill for many years.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with c 40m of drop and 76.92% Dominance based on the 52m spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website and an estimated bwlch height of c 12m based on contouring between 10m – 20m.  The summit height produced by the Trimble survey is 54.5m (converted to OSGM15) with its position to the west of where the 52m spot height appears and outside of the uppermost 50m ring contour on Ordnance Survey maps, with this summit height coming 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 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 a previous estimated summit height based on interpolation of contours.  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 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new summit height is 54.5m (converted to OSGM15) which is 2.5m higher than its previously listed height of 52m and 14.5m higher than the uppermost 40m ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Group:  Moelwynion

Summit Height (New Height):  54.5m (converted to OSGM15)

Name:  Bryn Tŵr

OS 1:50,000 map:  124

Summit Grid Reference:  SH 60453 44187

Drop:  c 43m

Dominance:  77.99%

Gathering data from the summit of Bryn Tŵr 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 (January 2018)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Gallt y Gog (SH 751 012) - 4th significant height revision

Survey post for Gallt y Gog

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, due to a survey with the Trimble GeoXH 6000 which took place on the 29^th October 2017 and conducted by Myrdyn Phillips.

The criteria for the two lists this height revision affects are:

30-99m Twmpau – Welsh hills at and above 30m and below 100m in height that have 30m minimum drop.  With the word Twmpau being an acronym standing for ‘thirty welsh metre prominences and upward’.

Y Trechol – The Dominant Hills of Wales - Welsh P30s whose prominence equal or exceed half that of their absolute height.

The name of the hill is Gallt y Gog and it is placed in the Pumlumon range of hills which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and the hill is positioned overlooking the A 489 road to its south and the Afon Dyfi to its north, with the town of Machynlleth at the base of the hill to the south. 

As the summit of the hill is not on designated open access land permission to visit should be sought, for those wishing to do so the nearest open access land is to the south-west of the hill, however there are paths in the conifer plantation that covers this hill’s summit and these indicate that people have visited this hill for many years.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with c 66m of drop and 72.53% dominance based on an estimated summit height of c 91m which was based on a 90m uppermost contour, and an estimated bwlch height of c 25m, with the summit height produced by the Trimble being 87.5m (converted to OSGM15), with this summit height coming 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 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 a previous estimated summit height based on interpolation of contours.  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 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

However, although the 5-15cm: 43.58% Estimated Accuracy recorded by the Trimble GeoXH 6000 is reasonable considering that the survey took place within a wood; the Standard Deviation of 0.5m signifies that the accuracy of the data set is questionable.  To compound this uncertainty there is question whether the uppermost 90m contour on Ordnance Survey maps is erroneous as it is placed a significant distance from where the accepted summit position of this hill is situated, according to the map the accepted summit position on the ground is above 80m but below the 90m contour.  However, this 90m uppermost contour could in fact be a depression and this ring contour signifies a 70m height, with the uppermost contour on Ordnance Survey maps being 80m, whatever the uncertainty, the result produced by the Trimble GeoXH 6000 for the summit of this hill does come within the above specified parameters. 

Therefore, this hill’s new summit height is 87.5m (converted to OSGM15) which is 3.5m lower than its previously estimated height of c 91m and 2.5m lower that what is thought to be the uppermost ring contour on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group:  Pumlumon

Name:  Gallt y Gog

OS 1:50,000 map:  135

Summit Height (New Height):  87.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 75169 01223 (Trimble GeoXH 6000)

Bwlch Height:  24.7m (LIDAR)

Bwlch Grid Reference:  SH 75589 00921 (LIDAR)

Drop:  62.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  71.74% (Trimble GeoXH 6000 summit and LIDAR bwlch)

The Trimble GeoXH 6000 gathering data at the summit of Gallt y Gog (SH 751 012) 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 (January 2018)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Emsger (SM 651 226) - 3rd significant height revision

Survey post for Emsger


There has been a Significant Height Revision to a hill that is listed in the Y Pellennig, 30-99m Twmpau and Y Trechol - The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that resulted in this height revision being conducted on the 14^th May 2016 in good, bright conditions, perched beside a lighthouse on one of the most remote places in the whole of Wales.

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

Y Pellennig –The Remotest Hills of Wales comprise all Welsh hills whose summit is 2.5km or more from the nearest paved public road and which have a minimum 15m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams.

30-99m Twmpau - These are the Welsh hills at or above 30m and below 100m in height that have a minimum drop of 30m.  The word Twmpau is an acronym for thirty welsh metre prominences and upward, and the list is authored by Myrddyn Phillips. 

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 list is authored by Myrddyn Phillips.

The hill is positioned on the island known as Emsger, which is also commonly known as South Bishop.  This island is positioned an approximate 8km (5 miles) west of St David’s Head in western Pembrokeshire, and unless being a competent and enthusiastic seal, it can only be approached by boat.  The island forms a part of the Bishops and Clerks chain of islands which form a compact groups of islets; all are rocky and are aligned northward to southward with North Bishop, Carreg Rhoson, Daufraich and Emsger being the main named island in each small group. 

The island is predominantly rock and if not for a series of steps leading up toward its summit its ascent would no doubt prove more problematic.  The upper part of Emsger has a lighthouse on it; this was built in 1839, and was converted to operating by electric in 1959, and demanned and automated in 1983.

The upper part of the island now has the lighthouse and associated buildings and platforms built on it, and therefore what once constituted the natural summit of the island is either buried under the lighthouse / platforms or it was destroyed during construction of the lighthouse.

I visited Emsger with Adrian Rayner, Ayako, Rob Woodall, Jon Glew, Sheila Glew, Sarah Kerr and Bob Kerr, and a quick assessment of what is left of natural ground pinpointed that this is situated just to the south-west of the main southerly corner of the lighthouse and its grounds.  This position was adjacent to steps leading down to the island’s helipad.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with a 37m summit height, which originates from the spot height on the Ordnance Survey 1:25,000 Explorer map, with the spot of this spot height positioned on the south-east part of the land immediately adjacent to the lighthouse.  This is on a part of the construction and is man-made; however natural ground exists close to this point but it is significantly lower.

Therefore this island’s new summit height is 33.8m (converted to OSGM15) which is 3.2m lower than its previously listed height of 37m which appears on Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Island:  Bishops and Clerks

Summit Height:  33.8m (converted to OSGM15)

Name:  Emsger

OS 1:50,000 map:  157

Summit Grid Reference:  SM 65116 22619

Drop:  33.8m (converted to OSGM15)

Dominance:  100.00%

The Trimble GeoXH 6000 gathering data 0.99m above the highest remaining natural ground at the summit of Emsger, otherwise known as South Bishop (SM 651 226) which resulted in this island's significant height revision

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

Myrddyn Phillips (June 2016)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Pt. 36.9, Ynys Hir (SH 566 398) - 2nd significant height revision

Summit survey post for Pt. 36.9, Ynys Hir

Bwlch survey post for Pt. 36.9, Ynys Hir

Hill Reclassifications post for Pt. 36.9, Ynys Hir 


There has been a Significant Height Revision in the 30-99m Sub-Twmpau (thirty welsh metre prominences and upward) list initiated by a survey with the Trimble GeoXH 6000, with the following details being retrospective as the  survey that resulted in this height revision was conducted on 1^st February 2014.

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


30-99m Twmpau - these are the Welsh hills at or above 30m and below 100m in height that have a minimum drop of 30m. 

30-99m Sub-Twmpau - these are the Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop

The listed name of the hill is Pt. 36.9m, Ynys Hir with its adjacent and higher hill taking on the full name without the point (Pt.) notation, and it is situated in the lowlands outside of Porthmadog in north-west Wales, and the survey was conducted in the company of Aled Williams who had suggested the walk, as he considered at least one of the hills he proposed for us to visit would become a new P30 – he was right!  With the new P30 being Ynys Hir (SH 56695 39393) which is adjacent to the hill this blog post relates to; Pt. 36.9m, Ynys Hir (SH 56649 39840).

The hill is situated to the north of Porthmadog in the area known as Traeth Mawr, and it can be accessed from a lay-by on the A487 to the south of the hill, however its ascent can be problematic due to the undergrowth.

The summit height of this hill has been dramatically increased from its current Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer 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 20m on both of these maps, with an estimated summit height of c 24m.  Its new summit height is 36.9m (converted to OSGM15), which is 12.9m higher than its previously estimated height and 16.9m higher than the 20m uppermost ring contour on current Ordnance Survey maps.

Although the new summit height of 36.9m (converted to OSGM15) is dramatically different to current Ordnance Survey map detail, the Ordnance Survey Historical 1:25,000 map has an uppermost ring contour of 100ft for this hill which is correct when compared to the surveyed height produced by the Trimble GeoXH 6000. 

The full details for the hill are:

Cardinal Hill:  Hir Ynys

Summit Height (New Height):  36.9m (converted to OSGM15)

Name:  Pt. 36.9m, Ynys Hir

OS 1:50,000 map:  124

Summit Grid Reference:  SH 56649 39840

  

Drop:  25.8m (converted to OSGM15)

Setting up the Trimble geoXH 6000 at the summit of Pt. 36.9m, Ynys Hir.  Photo: Aled Williams

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

For details on the bwlch survey that confirmed the drop value of this hill

Myrddyn Phillips (August 2015)

Mapping Mountains - Significant Height Revisions - 30-99m Twmpau

Ynys Hir (SH 566 396) - 1st significant height revision

Survey post for Ynys Hir

Hill Reclassifications post for Ynys Hir - 30-99m Twmpau

Hill Reclassifications post for Ynys Hir - Y Trechol - the Dominant Hills of Wales


There has been a Significant Height Revision to the 30-99m Twmpau and Y Trechol - The Dominant Hills of Wales listings initiated by a survey with the Trimble GeoXH 6000, with the following details being retrospective as the survey that resulted in this height revision was conducted on 1^st February 2014.

The two listings that this height revision affects are:


30-99m Twmpau - these are the Welsh hills at or above 30m and below 100m in height that have a minimum drop of 30m. 

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 Ynys Hir and it is situated in the lowlands outside of Porthmadog in north-west Wales, and the survey was conducted in the company of Aled Williams who had suggested the walk as he considered at least one of the hills he proposed for us to visit would become a new P30 – he was right!

The hill is situated to the north of Porthmadog in the area known as Traeth Mawr, and it can be easily accessed from a lay-by on the A487 to the south-west.  The term easily accessed is only applicable to where the road is situated in relation to the hill as it can be a bit of a battle to reach its top.

The summit height of Ynys Hir has been dramatically increased from its current Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer 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 20m on both of these maps, with an estimated summit height of c 23m.  Its new summit height is 37.3m (converted to OSGM15), which is 14.3m higher than its previously estimated height and 17.3m higher than the 20m uppermost ring contour on the current Ordnance Survey maps.

Although the new summit height of 37.3m (converted to OSGM15) is dramatically different to current Ordnance Survey map detail, the Ordnance Survey Historical 1:25,000 map has an uppermost ring contour of 100ft for this hill which is correct when compared to the surveyed height produced by the Trimble GeoXH 6000.  

The full details for the hill are:

Cardinal Hill:  Hir Ynys

Summit Height (New Height):  37.3m (converted to OSGM15)

Name:  Ynys Hir

OS 1:50,000 map:  124

Summit Grid Reference:  SH 56695 39693 

Drop:  c 34m

Dominance:  91.21%

Beyond the trees, vertical cliffs and undergrowth is the summit of Ynys Hir, a new P30 which has a significant height revision

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

Myrddyn Phillips (August 2015)