Mapping Mountains – Significant Height Revisions – 200m Twmpau

200m Twmpau – Significant Height Revisions

The 200m Twmpau (thirty welsh metre prominences and upward) are the Welsh hills at or above 200m and below 300m in height that have a minimum drop of 30m.  Accompanying the main P30 list is a sub list entitled the 200m Sub-Twmpau with the qualification to this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.

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

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Cae Gwar y Tŷ (SO 035 495) - 30th significant height revision

Survey post for Cae Gwar y Tŷ 

Summit Relocations post for Cae Gwar y Tŷ

Significant Name Changes post for Cae Gwar y Tŷ

 

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Cae Gwar y Tŷ (SO 035 495)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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. 

200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cae Gwar y Tŷ, and this was derived from the Tithe map, and it is adjoined to the Mynydd Epynt 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 west and immediate east, and the B4520 road farther to its east, and has the town of Llanfair-ym-Muallt (Builth Wells) towards the north.

When the original 200m 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 235m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 37m of drop, based on the 235m summit spot height and the 198m 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

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 Gwar y Tŷ (SO 035 495)

LIDAR analysis gives the summit of this hill as 232.8m positioned at SO 03502 49537 and SO 03504 49535, and when compared to its originally listed summit height of 235m this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 232.8m and this was derived from LIDAR analysis, this is 2.2m lower than the originally listed summit height of 235m, 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 Epynt 

Name:  Cae Gwar y Tŷ 

OS 1:50,000 map:  147

Summit Height (New Height):  232.8m (LIDAR) 

Summit Grid Reference:  SO 03502 49537 & SO 03504 49535 (LIDAR) 

Bwlch Height:  198.4m (LIDAR) 

Bwlch Grid Reference:  SO 03391 49083 (LIDAR) 

Drop:  34.4m (LIDAR) 

 

Myrddyn Phillips (February 2025)

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Pt. 277.7m (SO 106 406) - 29th significant height revision

Hill Reclassifications post for Pt. 277.7m

Significant Name Changes post for Pt. 277.7m

 

There has been a Significant Height Revision to a hill that is listed in the 200m 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 Pt. 277.7m (SO 106 406)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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. 

200m Twmpau by Myrddyn Phillips

The hill is being listed by the point (Pt. 277.7m) notation, and it is adjoined to the Mynydd Epynt 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 west and the A470 road to its east, and has the small community of Erwyd (Erwood) towards the north north-west.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying 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 18m of drop, based on the 275m summit spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map and an estimated c 257m bwlch height, based on interpolation of 10m contouring between 250m – 260m. 

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 Pt. 277.7m (SO 106 406)

LIDAR analysis gives the summit of hill as 277.7m positioned at SO 10666 40689, and when compared to its originally listed summit height of 275m 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 277.7m and this was derived from LIDAR analysis, this is 2.7m higher than the originally listed summit height of 275m, 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 Epynt 

Name:  Pt. 277.7m 

OS 1:50,000 map:  148, 161

Summit Height (New Height):  277.7m (LIDAR) 

Summit Grid Reference:  SO 10666 40689 (LIDAR) 

Bwlch Height:  255.1m (LIDAR) 

Bwlch Grid Reference:  SO 10264 40290 (LIDAR) 

Drop:  22.6m (LIDAR) 

 

Myrddyn Phillips (August 2024)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Comin Gwauncaegurwen (SN 721 131) - 28th significant height revision

Hill Reclassifications post for Comin Gwauncaegurwen

Summit Relocations post for Comin Gwauncaegurwen

Significant Name Changes post for Comin Gwauncaegurwen

 

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail produced by JoeNuttall in his surface analysis programme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Comin Gwauncaegurwen (SN 721 131)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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. 

200m Twmpau by Myrddyn Phillips

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

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the main P30 list or the accompanying Hills to be surveyed sub list, as with no significant contours of note on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map it was difficult to judge whether any hill of note existed. 

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

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

Extract from the interactive mapping hosted on the WalkLakes website

One of the mapping resources now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available maps and a 258m spot height is given on the summit area of this hill.  Latterly the contemporary Ordnance Survey 1:25,000 Explorer map now has an uppermost 250m contour for this hill. 

Extract from the contemporary online 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 Comin Gwauncaegurwen (SN 721 131)

LIDAR analysis gives the highest ground on this hill that could now be deemed natural as 258.4m positioned at SN 72135 13154, and when compared to detail on contemporary Ordnance Survey maps when the Welsh P30 lists were originated 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 258.4m and this was derived from LIDAR analysis, this is 34.4m higher than the uppermost 220m contour on the old Ordnance Survey 1:50,000 Landranger and 1:25,000 Outdoor Leisure map and 8.4m higher than the uppermost 250m contour that appears online on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Mynydd Du 

Name:  Comin Gwauncaegurwen 

OS 1:50,000 map:  160

Summit Height (New Height):  258.4m (LIDAR) 

Summit Grid Reference:  SN 72135 13154 (LIDAR) 

Bwlch Height:  218.5m (LIDAR) 

Bwlch Grid Reference:  SN 72505 12523 (LIDAR) 

Drop:  39.9m (LIDAR) 

 

Myrddyn Phillips (March 2024)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Mynydd Bach Brechfa (SN 520 286) - 27th significant height revision

Summit Relocations post for Mynydd Bach Brechfa

Significant Name Changes post for Mynydd Bach Brechfa

 

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail produced by Joe Nuttall in his surface analysis programme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Mynydd Bach Brechfa (SN 520 286)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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. 

200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Mynydd Bach Brechfa and this was derived from the Ordnance Survey series of Six-Inch maps, and it is adjoined to the Mynydd Pencarreg group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with the B4310 road to its north and west, and a minor road to its immediate south-east, and has the village of Brechfa towards the north north-east. 

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

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 category and listed with a 294m summit height, based on the spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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

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, with the uppermost contour being 295m, resulting in an estimated c 297m summit height based on interpolation and a summit relocation to SN 51818 28761.

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 Mynydd Bach Brechfa (SN 520 286)

LIDAR analysis gives the highest natural ground on this hill as 296.1m positioned at SN 52039 28618, and when compared to its originally listed summit height of 294m 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 296.1m and this was derived from LIDAR analysis, this is 2.1m higher than the originally listed summit height of 294m, which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Mynydd Pencarreg 

Name:  Mynydd Bach Brechfa 

OS 1:50,000 map:  146

Summit Height (New Height):  296.1m (LIDAR) 

Summit Grid Reference:  SN 52039 28618 (LIDAR) 

Bwlch Height:  223.7m (LIDAR) 

Bwlch Grid Reference:  SN 51351 28147 (LIDAR) 

Drop:  72.3m (LIDAR) 

 

Myrddyn Phillips (March 2024)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Cae’r Faen Mynach (SN 765 003) - 26th significant height revision

Hill Reclassifications post for Cae'r Faen Mynach

Significant Name Changes post for Cae'r Faen Mynach

 

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail produced by Joe Nuttall in his surface analysis programme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Cae'r Faen Mynach (SN 765 003)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cae’r Faen Mynach and this was derived from the Tithe map, and it is adjoined to the Fan Fawr group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with a minor road to its west, the A474 road farther to its west, the A4230 and A465 roads to its south and the A4109 road to its east, and has the village of Aberdulais towards the south-east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 category. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 27m of drop, based on the 234m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 207m bwlch height, based on interpolation of 10m contouring between 200m – 210m.

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'r Faen Mynach (SN 765 003) 

LIDAR analysis gives the highest ground on this hill as 237.6m positioned at SN 76549 00356, and when compared to its originally listed summit height of 234m 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 237.6m and this was derived from LIDAR analysis, this is 3.4m higher than the originally listed summit height of 234m, which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Fan Fawr 

Name:  Cae’r Faen Mynach 

OS 1:50,000 map:  170

Summit Height (New Height):  237.6m (LIDAR) 

Summit Grid Reference:  SN 76549 00356 (LIDAR) 

Bwlch Height:  207.0m (LIDAR) 

Bwlch Grid Reference:  SN 75759 01169 (LIDAR) 

Drop:  30.6m (LIDAR) 

 

Myrddyn Phillips (December 2023)

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Parc Uchaf Gwydyr (SH 792 597) - 25th significant height revision

Summit Relocations post for Parc Uchaf Gwydyr

 

There has been a Significant Height Revision to a hill that is listed in the 200m 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 Parc Uchaf Gwydyr (SH 792 597)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Parc Uchaf Gwydyr, and it is adjoined to the Carnedd Llywelyn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with a minor road to its north-west, the A5 road to its south-west, and the B5106 road to its east, and has the town of Betws-y-coed towards the south.

When the original 200m 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 272m, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at SH 79181 60064. 

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

When the accompanying sub list to the 200m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and its summit relocated to SH 79186 59729 and listed with an estimated height of c 274m.

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 Parc Uchaf Gwydyr (SH 792 597)

LIDAR analysis gives the highest ground on this hill as 276.7m positioned at SH 79204 59775, as opposed to its originally listed summit position which LIDAR analysis gives as 270.3m positioned at SH 79182 60067, 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 276.7m and this was derived from LIDAR analysis, this is 4.7m higher than the originally listed summit height of 272m, which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, and 2.7m higher than the previously listed summit height of c 274m, which was based on interpolation of the uppermost 270m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map.  

 

The full details for the hill are:

Group:  Carnedd Llywelyn 

Name:  Parc Uchaf Gwydyr 

OS 1:50,000 map:  115

Summit Height (New Height):  276.7m (LIDAR) 

Summit Grid Reference:  SH 79204 59775 (LIDAR) 

Bwlch Height:  225.2m (LIDAR) 

Bwlch Grid Reference:  SH 78923 59652 (LIDAR) 

Drop:  51.5m (LIDAR) 

 

Myrddyn Phillips (November 2023)

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Castell Dolforwyn (SO 151 950) - 24th significant height revision

Significant Name Changes post for Castell Dolforwyn

Survey post for Castell Dolforwyn

 

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey and LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Castell Dolforwyn (SO 151 950)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Castell Dolforwyn, and it is adjoined to the Carnedd Wen group of hills, which are situated in the southern part of North Wales (Region A, Sub-Region A3), and it is positioned encircled by minor roads, with the B4389 road farther to its south-west and the A483 road farther to its south-east, and has the town of Y Drenewydd (Newtown) towards the south-west.

When the original 200m 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 23om, with this being the uppermost contour on the contemporary Ordnance Survey 1:25,000 Explorer map. 

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 43m of drop, based on the 231m 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 188m bwlch height, based on interpolation of 5m contouring between 185m – 190m that also appeared on this mapping. 

The Trimble GeoXH 6000 gathering data at the summit of Castell Dolforwyn

However, it was not until the Trimble GeoXH 6000 survey that the details for this hill could be accurately re-assessed.  The summit height produced by this survey is 228.5m and is positioned at SO 15189 95016, 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 228.5m and this was derived from a Trimble GeoXH 6000 survey, this is 2.5m lower than the previously listed summit height of 231m, 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:  Carnedd Wen 

Name:  Castell Dolforwyn 

OS 1:50,000 map:  136

Summit Height (New Height):  228.5m (Trimble GeoXH 6000) 

Summit Grid Reference:  SO 15189 95016 (Trimble GeoXH 6000) 

Bwlch Height:  188.1m (LIDAR) 

Bwlch Grid Reference:  SO 14988 95278 (LIDAR) 

Drop:  40.4m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (November 2023)

 

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Gronglwyd (SN 598 558) - 23rd significant height revision

Significant Name Changes post for Gronglwyd

 

There has been a Significant Height Revision to a hill that is listed in the 200m 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 Gronglwyd (SN 598 558)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Gronglwyd and this was derived from the Tithe map, and it is adjoined to the Mynydd Bach group of hills, which are situated in the western part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north and west, and the A485 road to its south-east, and has the town of Tregaron towards the east north-east. 

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

When the original 200m 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 239m, based on the spot height that appeared on the 1985 Ordnance Survey 1:50,000 Landranger map (latterly updated with a 240m spot height). 

Extract from the contemporary 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 Gronglwyd (SN 598 558)

The height produced by LIDAR analysis to the summit of this hill is 240.3m positioned at SN 59868 55899, and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 240.3m and this was derived from LIDAR analysis, this is 1.3m higher than the originally listed summit height of 239m, which was based on the spot height that appears on the 1985 Ordnance Survey 1:50,000 Landranger map.

 

The full details for the hill are:

Group:  Mynydd Bach 

Name:  Gronglwyd 

OS 1:50,000 map:  146

Summit Height (New Height):  240.3m (LIDAR) 

Summit Grid Reference:  SN 59868 55899 (LIDAR) 

Bwlch Height:  208.1m (LIDAR) 

Bwlch Grid Reference:  SN 60305 55837 (LIDAR) 

Drop:  32.2m (LIDAR) 

 

Myrddyn Phillips (November 2022)

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Cae Pen Crug (SN 654 592) - 22nd significant height revision

Hill Reclassifications post for Cae Pen Crug

Summit Relocations post for Cae Pen Crug

Significant Name Changes post for Cae Pen Crug

 

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Cae Pen Crug (SN 654 592)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cae Pen Crug and this was derived from the Tithe map, and it is adjoined to the Mynydd Bach group of hills, which are situated in the western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north, the B4578 road to its west, the B4342 road to its south and the A485 road to its east, and has the town of Tregaron towards the east.

When the original 200m 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 224m based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 655 590. 

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 Cae Pen Crug (SN 654 592)

The height produced by LIDAR analysis to the summit of this hill is 229.1m positioned at SN 65493 59251, and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 229.1m and this was derived from LIDAR analysis, this is 5.1m higher than the previously listed summit height of 224m, which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Mynydd Bach 

Name:  Cae Pen Crug 

OS 1:50,000 map:  146

Summit Height (New Height):  229.1m (LIDAR) 

Summit Grid Reference:  SN 65493 59251 (LIDAR) 

Bwlch Height:  194.2m (LIDAR) 

Bwlch Grid Reference:  SN 65231 59601 (LIDAR) 

Drop:  34.9m (LIDAR) 

 

Myrddyn Phillips (October 2022)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Moel y Crio (SJ 199 696) - 21st significant height revision

Survey post for Moel y Crio

Hill Reclassifications post for Moel y Crio

Summit Relocations post for Moel y Crio

 

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips with assistance from Mark Trengove.

 

Moel y Crio (SJ 199 696)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Moel y Crio, and it is adjoined to the Moel y Gamelin group of hills, which are situated in the north-eastern part of North Wales (Region A, Sub-Region A2), and it is positioned encircled by minor roads with the B5123 road farther to its east, and has the town of Yr Wyddgrug (Mold) towards the south-east.

When the original 200m 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 14m of drop, based on the 292m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map at SJ 200 695 and an estimated c 278m bwlch height, based on interpolation of 5m contouring between 275m – 280m 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 the Trimble GeoXH 6000 survey that the details for this hill could be accurately re-assessed.  The summit height produced by this survey is 297.5m and is positioned at SJ 19988 69614, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

The Trimble GeoXH 6000 gathering data at the summit of Moel y Crio

Therefore, the new listed summit height of this hill is 297.5m and this was derived from a Trimble GeoXH 6000 survey, this is 5.5m higher than the previously listed summit height of 292m, 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:  Moel y Gamelin 

Name:  Moel y Crio 

OS 1:50,000 map:  116

Summit Height (New Height):  297.5m (converted to OSGM15) 

Summit Grid Reference:  SJ 19988 69614 

Bwlch Height:  276.8m (converted to OSGM15) 

Bwlch Grid Reference:  SJ 20406 69385 

Drop:  20.7m

 

Myrddyn Phillips (September 2022)

 

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Pen y Ddinas (SN 627 357) - 20th significant height revision

Summit Relocations post for Pen y Ddinas

 

There has been a Significant Height Revision to a hill that is listed in the 200m 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 Pen y Ddinas (SN 627 357)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m 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 y Ddinas and it is adjoined to the Mynydd Pencarreg group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north, the B4337 road to its south-west and the B4302 road to its east, and has the village of Llansawel towards the north-west.

When the original 200m 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 c 200m based on the uppermost contour on the contemporary 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 53m drop, based on an estimated c 207m summit height and an estimated c 154m bwlch height, with both heights based on interpolation of 10m contouring that appear on the contemporary Ordnance Survey 1:25,000 Explorer map. 

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

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

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 155m bwlch spot height and when coupled with a re-evaluation of its estimated summit height of c 203m, these values gave this hill an estimated c 48m of drop, which was still insufficient for Lesser Dominant status.

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 y Ddinas (SN 627 357)

The summit height produced by LIDAR analysis is 230.9m and is positioned at SN 62756 35746, 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 230.9m and this was derived from LIDAR analysis, this is 27.9m higher than the previously listed summit height of c 203m, which was based on re-evaluated interpolation of the uppermost 200m ring contour that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Mynydd Pencarreg

Name:  Pen y Ddinas

OS 1:50,000 map:  146

Summit Height (New Height):  230.9m (LIDAR)

Summit Grid Reference:  SN 62756 35746 (LIDAR)

Bwlch Height:  153.2m (LIDAR)

Bwlch Grid Reference:  SN 62239 35477 (LIDAR)

Drop:  77.7m (LIDAR)

Dominance:  33.63% (LIDAR)

 

Myrddyn Phillips (June 2022)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Fan (SN 672 315) - 19th significant height revision

Summit Relocations post for Fan

There has been a Significant Height Revision to a hill that is listed in the 200m 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 Fan (SN 672 315)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m 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 Fan, 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, north-east and south and the B4302 road to the south-west, and has the village of Llanwrda towards the east. 

When the original Welsh 200m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 265m summit height, based on the spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 67516 31466. 

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 267m summit spot height positioned at SN 67222 31598. 

Another of the mapping resources now available online is the Magic Maps website which hosts an interactive map originated from Ordnance Survey data.  This mapping also shows a 267m spot height in the same vicinity as the spot height on the Interactive Coverage Map. 

Extract from the Magic Maps website

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

LIDAR summit image of Fan (SN 672 315)

The summit height produced by LIDAR analysis is 268.7m 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 268.7m and this was derived from LIDAR analysis, this is 3.7m higher than the originally listed summit height of 265m which appears as a spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Mynydd Mallaen 

Name:  Fan 

OS 1:50,000 map:  146

Summit Height (New Height):  268.7m (LIDAR) 

Summit Grid Reference:  SN 67223 31597 (LIDAR) 

Bwlch Height:  175.4m (LIDAR) 

Bwlch Grid Reference:  SN 67061 31937 (LIDAR) 

Drop:  93.3m (LIDAR) 

Dominance:  34.71% 

 

Myrddyn Phillips (March 2022)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Allt Mes (SN 795 397) - 18th significant height revision

Hill Reclassifications post for Allt Mes

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Allt Mes (SN 795 397)

The criteria for the list this height revision affects are: 

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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. 

200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Allt Mes, and it is adjoined to the Drygarn Fawr group of hills, which are situated in the central part of the South Wales Region (Region B, Sub-Region B1), and it is positioned with minor roads to its north-east, north-west and south-west, and the A483 road to its south-east, and has the town of Llanymddyfri (Llandovery) towards the south south-west. 

When the original 200m 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 33m of drop, based on the 217m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 184m bwlch height, based on interpolation of 10m contouring between 180m – 190m 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. 

LIDAR summit image of Allt Mes (SN 795 397)

The summit height produced by LIDAR analysis is 219.4m 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, the new listed summit height of this hill is 219.4m and this was derived from LIDAR analysis, this is 2.4m higher than the originally listed summit height of 217m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Drygarn Fawr 

Name:  Allt Mes 

OS 1:50,000 map:  146, 160

Summit Height (New Height):  219.4m (LIDAR) 

Summit Grid Reference:  SN 79575 39715 (LIDAR) 

Bwlch Height:  182.8m (LIDAR) 

Bwlch Grid Reference:  SN 79199 39937 (LIDAR) 

Drop:  36.6m (LIDAR) 

 

Myrddyn Phillips (January 2022)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Quarry Field (SJ 155 075) - 17th significant height revision

Survey post for Quarry Field

Hill Reclassifications post for Quarry Field

Significant Name Changes post for Quarry Field

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Quarry Field (SJ 155 075)

The criteria for the list this height revision affects are: 

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Quarry Field and this was derived from the Tithe map, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with the B4392 road to its north-west and the A458 road to its south, and has the town of Y Trallwng (Welshpool) towards the east. 

When the original 200m 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. 

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 25m of drop, based on an estimated c 262m summit height and an estimated c 237m bwlch height, with both heights based on interpolation of 10m contouring that appear on the Ordnance Survey 1:25,000 Explorer map.  With an adjacent hill now listed as Cefn Uchaf (SJ 157 072) given a summit height of 262m based on the spot height that appears on contemporary Ordnance Survey 1:25,000 Explorer maps. 

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which 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 the area taking in this hill it also had contouring at 5m intervals with an uppermost 265m contour, with interpolation giving an estimated c 266m summit height and as this is higher than the 262m summit spot height given Cefn Uchaf the bylchau were swapped and each hill was reclassified. 

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 Quarry Field (SJ 155 075)

The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in 268.5m at SJ 15530 07552 and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

The Trimble GeoXH 6000 gathering data at the summit of Quarry Field

Therefore, this hill’s new listed summit height is 268.5m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SJ 15530 07552 and is 2.5m higher than the previously listed summit height of c 266m which was estimated from the uppermost 265m contour 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:  Carnedd Wen 

Name:  Quarry Field 

OS 1:50,000 map:  125

Summit Height (New Height):  268.5m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SJ 15530 07552 (Trimble GeoXH 6000) 

Bwlch Height:  209.6m (LIDAR) 

Bwlch Grid Reference:  SJ 16489 07601 (LIDAR) 

Drop:  58.9m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (June 2021)

 

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Banc y Maen Rochorlem (SN 675 691) - 16th significant height revision

Survey post for Banc y Maen Rochorlem

Hill Reclassifications post for Banc y Maen Rochorlem

Summit Relocations post for Banc y Maen Rochorlem

Significant Name Changes post for Banc y Maen Rochorlem

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

The summit of Banc y Maen Rochorlem (SN 675 691)

The criteria for the list this height revision affects are: 

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Banc y Maen Rochorlem and this was derived from the Tithe map, 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 A485 road to its west, the B4340 road to its north and east, and has the village of Lledrod towards the west north-west. 

When the original 200m 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-assessed and it was listed with an estimated c 28m of drop, based on an estimated c 296m summit height and an estimated c 268m bwlch height, with both heights based on interpolation of 10m contouring that appear on the Ordnance Survey 1:25,000 Explorer map.  With an adjacent hill now listed as Cae Pen y Maen (SN 656 694) given a summit height of 297m which was based on the spot height that appears on contemporary Ordnance Survey 1:25,000 Explorer maps. 

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which 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 299m spot height was given on the area of its summit and as this is higher than the 297m spot height given Cae Pen y Maen the bylchau were swapped and each hill was reclassified. 

The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in 299.3m at SN 67513 69184 and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

The Trimble GeoXH 6000 gathering data from the natural high point of Banc y Maen Rochorlem

Therefore, this hill’s new listed summit height is 299.3m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SN 67513 69184 and is 3.3m higher than its originally listed height of c 296m which was based on interpolation of the uppermost 290m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Elenydd 

Name:  Banc y Maen Rochorlem 

OS 1:50,000 map:  135

Summit Height (New Height):  299.3m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SN 67513 69184 (Trimble GeoXH 6000) 

Bwlch Height:  206.2m (LIDAR) 

Bwlch Grid Reference:  SN 69578 68344 (LIDAR) 

Drop:  93.1m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (April 2021)

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Stingwern Wood (SJ 145 000) - 15th significant height revision

Survey post for Stingwern Wood

Significant Name Changes post for Stingwern Wood

Summit Relocations post for Stingwern Wood

There has been a Significant Height Revision to a hill that is listed in the 200m 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 a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Stingwern Wood (SJ 145 000)

The criteria for the list this height revision affects are: 

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Stingwern Wood, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is encircled by minor roads with the B4390 road further to its north, the B4389 road further to its west and the A483 road further to its south-east, and has the village of Aberriw (Berriew) towards the east. 

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website the qualifying hill was included in the main P30 list with a summit height of 251m positioned at SJ 154 997, which was taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

After the accompanying sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 60m of drop, based on an estimated c 258m summit height and an estimated c 198m bwlch height, with both values based on interpolation of 10m contouring that appear on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, with the summit also relocated to SJ 145 000. 

The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in 260.0m at SJ 14514 00063 and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

The Trimble GeoXH 6000 gathering data at the summit of Stingwern Wood

Therefore, this hill’s new listed summit height is 260.0m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SJ 14514 00063 and is 2.0m higher than its previously listed height of c 258m and 9.0m higher than the origin qualifying listed summit of 251m, with the former based on interpolation of contours and the latter taken from the spot height on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Carnedd Wen

Name:  Stingwern Wood

OS 1:50,000 map:  136

Summit Height (New Height):  260.0m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SJ 14514 00063 (Trimble GeoXH 6000) 

Bwlch Height:  c 198m (interpolation) 

Bwlch Grid Reference:  SJ 14414 00402 (interpolation) 

Drop:  c 62m (Trimble GeoXH 6000 summit and interpolated bwlch) 

 

Myrddyn Phillips (March 2021)

 

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Castle Hill (SO 314 945) - 14th significant height revision

Survey post for Castle Hill

Hill Reclassifications post for Castle Hill

There has been a Significant Height Revision to a hill that is listed in the 200m 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, a Trimble GeoXH 6000 summit survey and subsequent LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Castle Hill (SO 314 945)

The criteria for the list this height revision affects are: 

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Castle Hill and it is adjoined to the Stiperstones group of hills, which straddle the border between Wales and England with the Welsh part of this group situated in the north-eastern part of South Wales (Region B, Sub-Region B2), and it is positioned with the A490 road to its west, the A489 road to its south and the A488 road to its east, and has the small community of Hyssington towards the south-west. 

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.  

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 24m of drop, based on an estimated c 281m summit height and the 257m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was named the Interactive Coverage Map. 

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

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

One of the mapping resources now available online is the Magic Maps website which hosts an interactive map originated from Ordnance Survey data.  This map has many spot heights not on other publicly available Ordnance Survey maps and for this hill a 283m spot height is given on the area of its summit. 

Extract from the Magic Maps website

The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in 283.2m at SO 31430 94540, and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

The Trimble GeoXH 6000 gathering data at the summit of Castle Hill

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

Therefore, the new listed summit height of this hill is 283.2m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SO 31430 94540 and is 2.2m higher than its originally listed height of c 281m which was estimated from the uppermost 280m contour on the contemporary Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Stiperstones 

Name:  Castle Hill 

OS 1:50,000 map:  137

Summit Height (New Height):  283.2m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SO 31430 94540 (Trimble GeoXH 6000) 

Bwlch Height:  258.6m (LIDAR) 

Bwlch Grid Reference:  SO 31415 94604 (LIDAR) 

Drop:  24.6m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (March 2021)

 

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Cow Pasture (SO 110 977) - 13th significant height revision

Survey post for Cow Pasture

Significant Name Changes post for Cow Pasture

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Cow Pasture (SO 110 977)

The criteria for the list this height revision affects are: 

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cow Pasture and this was derived from the Tithe map, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with the B4389 road to its south-west and minor roads to its north and east, and has the village of Tregynon towards the north-west. 

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the accompanying Hills to be surveyed sub list with a summit height of 213m, which was taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

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

LIDAR image of Cow Pasture

The result produced by LIDAR analysis gives this hill a 215.5m summit height, and as the summit has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes. 

The summit height and position produced by the Trimble GeoXH 6000 survey is 215.5m at SO 11094 97769, 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 summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. 

The Trimble GeoXH 6000 gathering data at the summit of Cow Pasture

Therefore, this hill’s new listed summit height is 215.5m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SO 11094 97769 and is 2.3m higher than its previously listed height of 213m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Carnedd Wen

Name:  Cow Pasture

OS 1:50,000 map:  136     

Summit Height (new height):  215.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SO 11094 97769 (Trimble GeoXH 6000) 

Bwlch Height:  190.2m (LIDAR)

Bwlch Grid Reference:  SO 11043 97985 (LIDAR)

Drop:  25.3m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (February 2021)

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Pt. 218.8m (SO 122 978) - 12th significant height revision

Survey post for Pt. 218.8m

Hill Reclassifications post for Pt. 218.8m

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

LIDAR image of Pt. 218.8m (SO 122 978)

The criteria for the list this height revision affects are: 

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The hill is being listed by the point (Pt. 218.8m) notation as an appropriate name for it either through local enquiry and / or historic research has not been found by the author, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with minor roads to its south-east and north, and has the B4389 road to its south-west, and has the small community of Betws Cedewain towards the south. 

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the accompanying Hills to be surveyed sub list, and listed with an estimated c 230m summit height. 

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 27m of drop, based on an estimated c 231m summit height and a 204m bwlch height, with the latter based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.  An anomaly was also noted with the heights given the contours on the upper part of this hill on the 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 result produced by LIDAR analysis gives this hill a 218.8m summit height and 13.6m of drop, confirming that the uppermost contour on the 1:25,000 Explorer map is not 230m, and as the summit has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes. 

LIDAR summit image of Pt. 218.8m (SO 122 978)

The summit height produced by the Trimble GeoXH 6000 survey is 218.8m, this is a dramatic height revision when compared to its previously listed height and comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

The Trimble GeoXH 6000 gathering data at the summit of Pt. 218.8m

Therefore, this hill’s new listed summit as surveyed with the Trimble GeoXH 6000 is 218.8m, this is positioned at SO 12216 97806 and is 12.2m lower than its previously listed height of c 231m which was based on what was presumed to be an uppermost 230m ring contour on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Carnedd Wen

Name:  Pt. 218.8m 

OS 1:50,000 map:  136

Summit Height (New Height):  218.8m (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SO 12216 97806 (Trimble GeoXH 6000) 

Bwlch Height:  205.3m (LIDAR) 

Bwlch Grid Reference:  SO 12899 97950 (LIDAR) 

Drop:  13.5m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (February 2021)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Pt. 275.1m (SO 131 995) - 11th significant height revision

Survey Post for Pt. 275.1m

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Pt. 275.1m (SO 131 995)

The criteria for the list this height revision affects are: 

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The hill is being listed by the point (Pt. 275.1m) notation as an appropriate name for it either through local enquiry and / or historic research has not been found by the author, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is encircled by minor roads, with the B4390 road to its north, the B4389 road to its west and the A483 road further to its south-east, and has the village of Tregynon towards the west south-west. 

When the original 200m 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 273m, which was taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

The summit height produced by the Trimble GeoXH 6000 survey is 275.1m, this is not a dramatic height revision when compared to some survey results, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

The Trimble GeoXH 6000 gathering data at the summit of Pt. 275.1m (SO 131 995)

Therefore, this hill’s new listed summit as surveyed with the Trimble GeoXH 6000 is 275.1m, this is positioned at SO 13195 99523 and is 2.1m higher than its previously listed height of 273m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Carnedd Wen

Name:  Pt. 275.1m

OS 1:50,000 map:  136

Summit Height (new height):  275.1m (converted to OSGM15)

Summit Grid Reference:  SO 13195 99523 

Bwlch Height:  241.3m (converted to OSGM15)

Bwlch Grid Reference:  SO 12737 99457

Drop:  33.8m

 

Myrddyn Phillips (January 2021)

 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Sixteen Acres (SO 120 987) - 10th significant height revision

Survey Post for Sixteen Acres

Hill Reclassifications post for Sixteen Acres

Significant Name Changes post for Sixteen Acres

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Sixteen Acres (SO 120 987)

The criteria for the list this height revision affects are: 

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Sixteen Acres and this was derived from local enquiry, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with the B4390 road to its north, the B4389 road to its west and the A483 road further to its south-east, and has the village of Tregynon towards the west. 

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 20m of drop, based on an estimated c 216m summit height and the 196m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was named the Interactive Coverage Map. 

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

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

LIDAR image of Sixteen Acres

The result produced by LIDAR analysis gives this hill a 219.2m summit height, and as the summit has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes. 

The Trimble GeoXH 6000 gathering data at the summit of Sixteen Acres

The summit height and position produced by the Trimble GeoXH 6000 survey is 219.2m at SO 12005 98756, 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 summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. 

Therefore, this hill’s new listed summit height is 219.2m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SO 12005 98756 and is 3.2m higher than its previously listed height of c 216m which was estimated from interpolation of its uppermost ring contour that appears on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Carnedd Wen

Name:  Sixteen Acres

OS 1:50,000 map:  136

Summit Height (new height):  219.2m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SO 12005 98756 (Trimble GeoXH 6000) 

Bwlch Height:  199.1m (LIDAR)

Bwlch Grid Reference:  SO 11953 98547 (LIDAR)

Drop:  20.1m (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (January 2021) 

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Crasty Frain (SO 109 983) - 9th significant height revision

Survey post for Crasty Frain

Hill Reclassifications post for Crasty Frain

Summit Relocations post for Crasty Frain

Significant Name Changes post for Crasty Frain

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill initially confirmed by LIDAR analysis instigated by Joe Nuttall who produced a summit analysis programme, with the LIDAR analysis initially conducted by Jim Bloomer and subsequently by Myrddyn Phillips, with the summit later surveyed with the Trimble GeoXH 6000 and which was conducted by Myrddyn Phillips.

Crasty Frain (SO 109 983)

The criteria for the list this height revision affects are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.

The 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Crasty Frain and this was derived from the Tithe map, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned with a minor road to its north and the B4389 road to its south-west, and has the village of Tregynon towards the west north-west.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the accompanying Hills to be surveyed sub list, and listed with a 253m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at SO 107 981.

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 27m of drop, based on the 253m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 226m bwlch height, with the latter based on interpolation of 10m contouring between 220m – 230m.

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 Crasty Frain

The height revision of this hill was initiated by Joe Nuttall who produced a summit analysis programme that used LIDAR with analternative height map (DEM) allowing identification of summits and cols and thereby drops.  The resulting spreadsheet that Joe produced contains over 29,600 hills.

This spreadsheet is being evaluated by a number of people, and for this particular hill it was Jim Bloomer who initially assessed this hill’s data against that produced via LIDAR.  Myrddyn Phillips then evaluated the details for this hill via LIDAR analysis and confirmed its summit height and position and hence its height revision and reclassification to 200m Twmpau status.  The summit of this hill has now been surveyed with the Trimble GeoXH 6000 and it is this evaluation on the hill and the subsequent survey that is being prioritised.

The Trimble GeoXH 6000 gathering data at the summit of Crasty Frain

The summit height and position produced by the Trimble GeoXH 6000 survey is 256.3m at SO 10995 98318, 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 summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, this hill’s new listed summit height is 256.3m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SO 10995 98318 and is 3.3m higher than its previously listed height of 253m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Carnedd Wen

Name:  Crasty Frain

OS 1:50,000 map:  136

Summit Height (new height):  256.3m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SO 10995 98318 (Trimble GeoXH 6000)

Bwlch Height:  226.1m (LIDAR)

Bwlch Grid Reference:  SO 10787 98754 (LIDAR)

Drop:  30.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips (October 2020)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Mynydd Llwyd (ST 433 935) - 8th significant height revision

Significant Name Changes post for Mynydd Llwyd

There has been a Significant Height Revision to a hill that is listed in the 200m 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 derived from detail on contemporary and historic Ordnance Survey maps.

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.

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

The name the hill is listed by is Mynydd Llwyd 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 A449 road to its west, the A48 road to its south and the B4235 road to its north-east, and has the city of Casnewydd (Newport) towards the west south-west.

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

When the original 200m 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 under the name of Gray Hill and listed with a 273m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating; 275m on 1986 1:50000 map.

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

Since publication of these P30 lists on Geoff Crowder’s v-g.me website there have been a number of Ordnance Survey maps made available online, some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website, and it is this scale of mapping that shows a 901.8ft (274.9m) Surface Height on the summit area of this hill.  It is this height that has been rounded up and appears as the 275m spot height on contemporary Ordnance Survey 1:50,000 Landranger maps.

Extract from the Ordnance Survey series of Six-Inch maps

As the Surface Height is more accurate than the 273m spot height which has been ascertained from photogrammetry, the 275m height is now used for this hill, 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 summit height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. 

Therefore, this hill’s new listed summit height is 275m and this was derived from the spot height that appears on the Ordnance Survey 1:50,000 Landranger map, which in itself has been derived from the Surface Height on the Ordnance Surveys series of Six-Inch maps.

The full details for the hill are:

Group:  Gwent Is Coed

Name:  Mynydd Llwyd

OS 1:50,000 map:  171, 172

Summit Height (New Height):  275m (spot height)

Summit Grid Reference:  ST 43399 93559 (hand-held GPS via DoBIH)

Bwlch Height:  c 183m (interpolation)

Bwlch Grid Reference:  ST 42894 93984 (interpolation)

Drop:  c 92m (spot height summit and interpolated bwlch)

Dominance:  33.45% (spot height summit and interpolated bwlch)

Myrddyn Phillips (May 2020)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Coed y Bwnydd (SO 366 069) - 7th significant height revision

Hill Reclassifications post for Coed y Bwnydd

Significant Name Changes post for Coed y Bwnydd

Summit Relocations post for Coed y Bwnydd

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Coed y Bwnydd (SO 366 069)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.

200m 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 Coed y Bwnydd and it is adjoined to the Mynyddoedd Duon group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Wysg (River Usk) and the B4598 road to its west, the A40 road to its north and the A449 road to its east, and has the village of Raglan towards the east north-east and the town of Brynbuga (Usk) towards the south south-east.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the main P30 list under the name of Clytha Hill and listed with a 196m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map at SO 368 069.

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and gives a second 196m spot height on the summit area of this hill and positioned at SO 367 069.  This additional 196m spot height also appears on Ordnance Survey data available on the Magic Maps website.

Extract from the Magic Maps website

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

                                        

LIDAR summit image of Coed y Bwnydd (SO 366 069)

The summit height produced by LIDAR analysis is 201.4m positioned at SO 36613 06919, this is a relatively substantial revision compared to some revised heights, and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 201.4m and this was produced by LIDAR analysis, this is 5.4m higher than its previously listed height of 196m which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the online Vector Map Local.

The full details for the hill are:

Group:  Mynyddoedd Duon

Name:  Coed y Bwnydd

OS 1:50,000 map:  161

Summit Height (New Height):  201.4m (LIDAR)

Summit Grid Reference:  SO 36613 06919 (LIDAR)

Bwlch Height:  59.4m (LIDAR)

Bwlch Grid Reference:  SO 39308 08901 (LIDAR)

Drop:  142.0m (LIDAR)

Dominance:  70.50%

Myrddyn Phillips (February 2020)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Allt Wen (SH 745 772) - 6th significant height revision

Survey post for Allt Wen

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height and its location, the drop and status of the hill confirmed by LIDAR analysis, and a subsequent survey with the Trimble GeoXH 6000, both conducted by Myrddyn Phillips with the latter taking place on the 15^th October 2018.

Allt Wen (SH 745 772)

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

200m Twmpau - Welsh hills at or above 200m and below 300m in height with 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

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

The name of the hill is Allt Wen, and it is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A55 road and the coast to its north, and has the town of Conwy towards its east.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 255m summit height based on the 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

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

LIDAR image of Allt Wen

The summit height produced by the Trimble GeoXH 6000 survey is 252.3m,  this is not a substantial revision when compared to some revised heights, and 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.

The Trimble GeoXH 6000 gathering data at the summit of Allt Wen

Therefore, this hill’s new listed summit height is 252.3m and this was produced by surveying with the Trimble GeoXH 6000, this is 2.7m lower than its previously listed height of 255m which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group:  Carneddau

Name:  Allt Wen

OS 1:50,000 map:  115

Summit Height (New height):  252.3m (converted to OSGM15)

Summit Grid Reference:  SH 74546 77264  

Bwlch Height:  160.2m (converted to OSGM15)

Bwlch Grid Reference:  SH 74855 77154

Drop:  92.1m

Dominance:  36.51%

For details on the survey of Allt Wen

Myrddyn Phillips (April 2019)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Mynydd y Dref (SH 759 777) - 5th significant height revision

Survey post for Mynydd y Dref

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, its location and the drop of the hill confirmed by LIDAR analysis, and a subsequent summit and bwlch survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter taking place on the 15^th October 2018.

Mynydd y Dref (SH 759 777)

LIDAR image of Mynydd y Dref

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The name of the hill is Mynydd y Dref, and it is adjoined to the Carneddau range of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A55 road and the coast to its north, and has the town of Conwy towards its east south-east.

When the original Welsh 200m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 244m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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

The summit height produced by the Trimble GeoXH 6000 survey is 246.1m, this is not a substantial 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.

The summit of Mynydd y Dref

Therefore, this hill’s new listed summit height is 246.1m and this was produced by surveying with the Trimble GeoXH 6000, this is 2.1m higher than its previously listed height of 244m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Carneddau

Name:  Mynydd y Dref

OS 1:50,000 map:  115

Summit Height (New height):  246.1m (converted to OSGM15)

Summit Grid Reference:  SH 75981 77799

  

Bwlch Height:  186.7m (converted to OSGM15)

Bwlch Grid Reference:  SH 75246 77548

Drop:  59.4m

For details on the survey of this hill

Myrddyn Phillips (April 2019)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Coed Eryr (SH 636 508) - 4th significant height revision

Survey post for Coed Eryr

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, its location and the drop of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter taking place on the 6^th October 2018.

LIDAR image of Coed Eryr

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The name of the hill is Coed Eryr, and it is adjoined to the Moelwynion range of hills, which are situated in the western part of North Wales (Region A, Sub-Region A1), and it is positioned between the lakes of Llyn Dinas to ts south-west and Llyn Gwynant to its north-east, with the A498 road to its north-west, and has the village of Beddgelert towards the south-west.

When the original Welsh 200m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 241m summit height 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

LIDAR summit image of Coed Eryr

The summit height produced by the Trimble GeoXH 6000 survey is 243.7m (converted to OSGM15), this is not a substantial 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 listed summit height is 243.7m (converted to OSGM15) and this was produced by surveying with the Trimble GeoXH 6000, this is 2.7m higher than its previously listed height of 241m which appears as a spot height on the Ordnance Survey 1:50,000 Landranger map.

The Trimble GeoXH 6000 gathering data at the summit of Coed Eryr

The full details for the hill are:

Group:  Moelwynion

Name:  Coed Eryr

OS 1:50,000 map:  115

Summit Height (New height):  243.7m (converted to OSGM15)

Summit Grid Reference:  SH 63612 50890

  

Bwlch Height:  181.6m (LIDAR)

Bwlch Grid Reference:  SH 64230 51021 (LIDAR)

Drop:  62.1m (Trimble summit and LIDAR bwlch)

For details on the summit survey of this hill

Myrddyn Phillips (March 2019)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Clip y Gylfinhir (SH 223 284) - 3rd significant height revision

1st survey of Clip y Gylfinhir

2nd summit survey of Clip y Gylfinhir

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the hill’s height, drop and status confirmed by a survey with the Trimble GeoXH 6000 which was conducted by Myrddyn Phillips on the 28^th December 2014 and 3^rd October 2018 in good, clear conditions with hardly a breath of breeze.

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The name of the hill is Clip y Gylfinhir, and it is adjoined to the Pen Llŷn range of hills, which are situated in the western part of North Wales (Region A, Sub-Region A1), and it is positioned toward the western end of Pen Llŷn, and is encircled by a series of minor roads and has the small community of Y Rhiw towards the south.

Clip y Gylfinhir (SH 223 284)

As the summit of the hill is a part of designated open access land it can be approached from most directions, with public footpaths leading in to the access land from a variety of directions, and for those wishing a quick ascent of the hill there is parking space at the immediate base of the hill to its north-east.

When the original Welsh 200m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed in the accompanying Hills to be surveyed sub list with a 270m summit height which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

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

The summit height produced by The Trimble GeoXH 6000 survey is 267.8m (converted to OSGM15), this is not a substantial 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.

The Trimble GeoXH 6000 gathering data at the summit of Clip y Gylfinhir

Therefore, this hill’s new summit height is 267.8m (converted to OSGM15) and this was produced by surveying with the Trimble GeoXH 6000, this is 2.3m lower than its previously listed height of 270m 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.

The full details for the hill are:

Group:  Pen Llŷn

Name:  Clip y Gylfinhir

OS 1:50,000 map:  123

Summit Height (New height):  267.8m (converted to OSGM15)

Summit Grid Reference:  SH 22395 28472

  

Bwlch Height:  240.1m (converted to OSGM15)

Bwlch Grid Reference:  SH 22514 28524

Drop:  27.7m (converted to OSGM15)

For details on the 1^st survey of this hill

For details on the 2nd survey that significantly revised the summit height of this hill

Myrddyn Phillips (December 2018)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Winllan Hill (SJ 217 214) - 2nd significant height revision 

1st summit survey post for Winllan Hill

2nd summit survey post for Winllan Hill

Summit Relocations post for Winllan Hill


There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau initiated by a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted over two days; 28^th / 29^th August 2015.

The listing that this height revision affects is:

200m Twmpau - These are the Welsh hills at or above 200m and below 300m in height that have a minimum drop of 30m.  The word Twmpau is an acronym for thirty welsh metre prominences and upward.

The name of the hill is Winllan Hill and it is situated in the lower easterly hills of Y Berwyn, and is positioned above Llansanffraid-ym-Mechain which is situated beside where the Afon Cain flows in to the Afon Efyrnwy (River Vyrnwy).  The hill was initially surveyed in the late evening in the company of Mark Trengove after nourishing our appetite in the Bradford Arms in Llanymynech.

Access to Winllan Hill is good as public footpaths from the south, west, north and east head towards its summit and parking is easily found when approaching the hill from the west and north, this is also likely to be the case if approaching the hill from the east and south.  The high point of the hill is beside a fence and under a large overhanging tree, and is only a few metres from where a public footpath crosses the field that the summit is situated in.

Prior to the survey with the Trimble GeoXH 6000 the hill was listed as 216m high based on the spot height on the area of the summit that appears on the Ordnance Survey 1:25,000 Explorer map, and an estimated drop value of c 48m, based on bwlch contour interpolation which gives the height of the bwlch as c 168m.  However, there is significantly higher land to the north of where the 216m spot height is positioned on the ground.  With the height resulting from the survey of the summit with the Trimble GeoXH 6000 being 220.3m (converted to OSGM15).  

Therefore this hill’s new summit height is 220.3m (converted to OSGM15) which is 4.3m higher than the previously listed height of 216m which was based on the Ordnance Survey 1:25,000 Explorer map spot height.

The full details for the hill are:

Cardinal Hill:  Rhialgwm

Summit Height (New Height):  220.3m (converted to OSGM15)

Name:  Winllan Hill

OS 1:50,000 map:  126

Summit Grid Reference:  SJ 21709 21460 

Drop:  c 52m

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

For details on the 1st survey that when combined with the 2nd survey significantly revised the summit height of this hill

For details on the 2nd survey that when combined with the 1st survey significantly revised the summit height of this hill

Myrddyn Phillips (October 2015)

Mapping Mountains - Significant Height Revisions - 200m Twmpau

Pen y Berth (SJ 081 127) - 1st significant height revision 

Summit survey post for Pen y Berth

Bwlch survey post for Pen y Berth 

Summit Relocations post for Pen y Berth


There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau (thirty welsh metre prominences and upward) as well as Y Trechol - the Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted on 19^th October 2014.

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


200m Twmpau - these are the Welsh hills at or above 200m and below 300m 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.  With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The name of the hill is Pen y Berth and it is situated in the Y Berwyn range of hills and the survey with the Trimble GeoXH 6000 was conducted in the company of Mark Trengove on a colourful autumnal day in October.

The hill can be accessed from 1km east of the small community of Dolanog on a track that heads north-west and then east to sneak up to the summit from the opposing side of the hill.  The summit area of the hill is given two 280m uppermost ring contours aligned east and west of one another on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, with each contour ring given a 282m spot height on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The following results are those obtained with the Trimble GeoXH 6000 for the two points surveyed:

Eastern 282m spot height:  283.7m (converted to OSGM15) at SJ 08322 12748

Western 282m spot height at SJ 08012 12780 not surveyed

Easterly high point of western 280m ring contour:  287.5m (converted to OSGM15) at SJ 08126 12730

The land at SJ 08126 12730 was visually judged to be higher than the land at SJ 08012 12780, therefore the latter position was not surveyed.  The height given this hill on the Ordnance Survey enlarged mapping hosted on the Geograh website is 282m, with the height resulting from the survey with the Trimble GeoXH 6000 being 287.5m (converted to OSGM15).

Therefore this hill’s new summit height is 5.5m higher than its previously listed height which came from the 282m spot height on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The full details for the hill are:

Cardinal Hill:  Carreg y Big

Summit Height (New Height):  287.5m (converted to OSGM15)

Name:  Pen y Berth

OS 1:50,000 map:  125

Summit Grid Reference:  SJ 08126 12730 

Drop:  134.2m (converted to OSGM15)

Dominance:  46.68%

Pen y Berth (SJ 081 127) a hill whose height has been significantly revised

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

Myrddyn Phillips (August 2015)