Mapping Mountains – Significant Height Revisions – 200m Twmpau

Chwarel Penrhyn (SH 621 658) 

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 Chwarel Penrhyn (SH 621 658)

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.  The list is authored by Myrddyn Phillips, 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 Chwarel Penrhyn, and it is adjoined to the Glyder Fawr 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 B4409 road to its north, a minor road to its west and the A5 road to its east, and has the town of Bethesda towards the north-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 accompanying Hills to be surveyed sub list, as with no significant contours of note on the contemporary Ordnance Survey 1:25,000 map, it was hard to know whether any hill with qualifying prominence existed and therefore it was considered not to meet the criteria then used for this sub category. 

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 Chwarel Penrhyn (SH 621 658)

LIDAR analysis gives the summit of this hill as 220.6m positioned at SH 62149 65875, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 220.6m and this was derived from LIDAR analysis, this is 70.6m higher than the highest contour in the vicinity of this hill that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Glyder Fawr 

Name:  Chwarel Penrhyn 

OS 1:50,000 map:  115

Summit Height (New Height):  220.6m (LIDAR) 

Summit Grid Reference:  SH 62149 65875 (LIDAR) 

Bwlch Height:  197.0m (LIDAR) 

Bwlch Grid Reference:  SH 61793 65966 (LIDAR) 

Drop:  23.6m (LIDAR)

Myrddyn Phillips (January 2026) 

Mapping Mountains – Significant Height Revisions – 200m Twmpau

Coed Bryn y Garth Lwyd (SH 725 576) 

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 Coed Bryn y Garth Lwyd (SH 725 576)

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.  The list is authored by Myrddyn Phillips, 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 Coed Bryn y Garth Lwyd, and this was derived from the Ordnance Survey series of Six-Inch maps, and it is adjoined to the Moel Siabod group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A2), and it is positioned with the A5 road to its north and the A4086 road to its west north-west, and has the village of Capel Curig 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 accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category, as with no significant contours of note on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map it was difficult to know whether any hill of note existed. 

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

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

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 for this hill it shows an uppermost 200m ring contour and bwlch contouring between 180m – 190m. 

Extract from the interactive mapping hosted on the WalkLakes 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 Bryn y Garth Lwyd (SH 725 576)

LIDAR analysis gives the summit of this hill as 202.2m positioned at SH 72557 57676, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 202.2m and this was derived from LIDAR analysis, this is 22.2m higher than the highest contour in the vicinity of this hill that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Moel Siabod 

Name:  Coed Bryn y Garth Lwyd 

OS 1:50,000 map:  115

Summit Height (New Height):  202.2m (LIDAR) 

Summit Grid Reference:  SH 72557 57676 (LIDAR) 

Bwlch Height:  179.7m (LIDAR) 

Bwlch Grid Reference:  SH 72372 57543 (LIDAR) 

Drop:  22.55m (LIDAR) 

 

Myrddyn Phillips (July 2025)

  

Mapping Mountains – Significant Height Revisions – 200m Twmpau

Ffridd Rhiwlwyfen (SN 758 986) 

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 Ffridd Rhiwlwyfen (SN 758 986)

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.  The list is authored by Myrddyn Phillips, 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 Ffridd Rhiwlwyfen, and it is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its west and east, the A489 road to its north and the A487 road to its north-west, and has the town of Machynlleth 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 included in the main P30 list with a 278m 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 an estimated c 72m of drop, based on the 278m summit spot height and an estimated c 206m bwlch height, based on interpolation of 10m contouring between 200m – 210m. 

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 Ffridd Rhiwlwyfen (SN 758 986)

LIDAR analysis gives the height of this hill as 280.0m positioned at SN 75800 98654, and when compared to its originally listed summit height of 278m 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 280.0m and this was derived from LIDAR analysis, this is 2.0m higher than the originally listed summit height of 278m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Banc Llechwedd Mawr 

Name:  Ffridd Rhiwlwyfen                  

OS 1:50,000 map:  135

Summit Height (New Height):  280.0m (LIDAR) 

Summit Grid Reference:  SN 75800 98654 (LIDAR) 

Bwlch Height:  205.5m (LIDAR) 

Bwlch Grid Reference:  SN 75435 97713 (LIDAR) 

Drop:  74.5m (LIDAR) 

 

Myrddyn Phillips (April 2025)

  

Mapping Mountains – Significant Height Revisions – 200m Twmpau

Cae Gwar y Tŷ (SO 035 495) 

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.

 

ills of Wales, and are reproduced below@

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) 

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.

 

ills of Wales, and are reproduced below@

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)