Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

 

30-99m Twmpau – Hill Reclassifications

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

The list is authored by Myrddyn Phillips and the posts that have appeared on Mapping Mountains detailing the additions, reclassifications and deletions to the main P30 list and the sub lists appear below presented chronologically in receding order.

Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

Carreg Rhoson (SM 671 256) – Double Sub-Twmpau addition (150th reclassification)

 

There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height and its location, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

Carreg Rhoson (SM 67173 25624) - the island on the right

The criteria for the list that this addition applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Carreg Rhoson, and it is adjoined to the Garn Fawr group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it forms part of an islet chain positioned to the west of mainland Wales with a minor road on the mainland to its east, and has the city of Tyddewi (St David’s) on the mainland also towards the east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was 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 island were re-evaluated and it was listed with 22m of drop, based on the 22m summit 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 Carreg Rhoson (SM 67173 25624)

Therefore, the confirmation of the addition of this hill to Double Sub-Twmpau status is due to LIDAR analysis, resulting in a 21.2m summit height and as this hill is an island, this value also gives it 21.2m of drop, which is sufficient for it to be classified as a Double Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Garn Fawr 

Name:  Carreg Rhoson 

OS 1:50,000 map:  157

Summit Height:  21.2m (LIDAR) 

Summit Grid Reference:  SM 67173 25624 (LIDAR)               

Bwlch Height:  N/A (sea level) 

Bwlch Grid Reference:  N/A (sea level) 

Drop:  21.2m (LIDAR) 

 

Myrddyn Phillips (December 2025)

Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

Carreg Rhoson (SM 673 257) – Double Sub-Twmpau addition (149th reclassification)

 

There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height and its location, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

Carreg Rhoson (SM 67343 25747) - the island on the left

The criteria for the list that this addition applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Carreg Rhoson, and it is adjoined to the Garn Fawr group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it forms part of an islet chain positioned to the west of mainland Wales with a minor road on the mainland to its east, and has the city of Tyddewi (St David’s) on the mainland also towards the east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was 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 island were re-evaluated and it was listed with 24m of drop, based on the 24m summit 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 Carreg Rhoson (SM 67343 25747) - the island on the right

Therefore, the confirmation of the addition of this hill to Double Sub-Twmpau status is due to LIDAR analysis, resulting in a 23.4m summit height and as this hill is an island, this value also gives it 23.4m of drop, which is sufficient for it to be classified as a Double Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Garn Fawr 

Name:  Carreg Rhoson 

OS 1:50,000 map:  157

Summit Height:  23.4m (LIDAR) 

Summit Grid Reference:  SM 67343 25747 (LIDAR)               

Bwlch Height:  N/A (sea level) 

Bwlch Grid Reference:  N/A (sea level) 

Drop:  23.4m (LIDAR) 

 

Myrddyn Phillips (December 2025)

Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

North Bishop (SM 666 277) – Double Sub-Twmpau deletion (148th reclassification)

 

There has been a deletion to the list of 30-99m Twmpau, with the summit height and its location, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of North Bishop (SM 666 277)

The criteria for the list that this deletion applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is North Bishop, and it is adjoined to the Garn Fawr group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it forms part of an islet chain positioned to the west of mainland Wales with a minor road on the mainland to its east south-east, and has the city of Tyddewi (St David’s) on the mainland also towards the east south-east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was 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 island were re-evaluated and it was listed with 22m of drop, based on the 22m summit 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.

Therefore, the deletion of this hill from Double Sub-Twmpau status is due to LIDAR analysis, resulting in a 19.1m summit height and as this hill is an island, this value also gives it 19.1m of drop, which is insufficient for it to be classified as a Double Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Garn Fawr 

Name:  North Bishop 

OS 1:50,000 map:  157

Summit Height:  19.1m (LIDAR) 

Summit Grid Reference:  SM 66654 27786 (LIDAR)               

Bwlch Height:  N/A (sea level) 

Bwlch Grid Reference:  N/A (sea level) 

Drop:  19.1m (LIDAR) 

 

Myrddyn Phillips (November 2025)

Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

North Bishop (SM 667 278) – Double Sub-Twmpau deletion (147th reclassification)

 

There has been a deletion to the list of 30-99m Twmpau, with the summit height and its location, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of North Bishop (SM 667 278)

The criteria for the list that this deletion applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is North Bishop, and it is adjoined to the Garn Fawr group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it forms part of an islet chain positioned to the west of mainland Wales with a minor road on the mainland to its east south-east, and has the city of Tyddewi (St David’s) on the mainland also towards the east south-east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was 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 island were re-evaluated and it was listed with 21m of drop, based on the 21m summit 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.

Therefore, the deletion of this hill from Double Sub-Twmpau status is due to LIDAR analysis, resulting in an 18.2m summit height and as this hill is an island, this value also gives it 18.2m of drop, which is insufficient for it to be classified as a Double Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Garn Fawr 

Name:  North Bishop 

OS 1:50,000 map:  157

Summit Height:  18.2m (LIDAR) 

Summit Grid Reference:  SM 66793 27882 (LIDAR)               

Bwlch Height:  N/A (sea level) 

Bwlch Grid Reference:  N/A (sea level) 

Drop:  18.2m (LIDAR) 

 

Myrddyn Phillips (November 2025)

Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

North Bishop (SM 672 281) – Double Sub-Twmpau deletion (146th reclassification)

 

There has been a deletion to the list of 30-99m Twmpau, with the summit height and its location, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

North Bishop (SM 672 281)

The criteria for the list that this deletion applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is North Bishop, and it is adjoined to the Garn Fawr group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it forms part of an islet chain positioned to the west of mainland Wales with a minor road on the mainland to its east south-east, and has the city of Tyddewi (St David’s) on the mainland also towards the east south-east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was 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 island were re-evaluated and it was listed with 24m of drop, based on the 24m summit 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 North Bishop (SM 672 281)

Therefore, the deletion of this hill from Double Sub-Twmpau status is due to LIDAR analysis, resulting in a 19.8m summit height and as this hill is an island, this value also gives it 19.8m of drop, which is insufficient for it to be classified as a Double Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Garn Fawr 

Name:  North Bishop 

OS 1:50,000 map:  157

Summit Height:  19.8m (LIDAR) 

Summit Grid Reference:  SM 67289 28179 (LIDAR)               

Bwlch Height:  N/A (sea level) 

Bwlch Grid Reference:  N/A (sea level) 

Drop:  19.8m (LIDAR) 

 

Myrddyn Phillips (October 2025)

Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

Pig Stone (SM 713 092) – Double Sub-Twmpau addition (145th reclassification)

 

There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height and its location, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pig Stone (SM 713 092)

The criteria for the list that this addition applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Pig Stone, and it is adjoined to the Garn Fawr group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned adjacent to the western coast of the island of Skomer with a minor road on the mainland to its east, and has the village of Marloes on the mainland also towards the east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was 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 island were re-evaluated and it was listed with 27m of drop, based on the 27m summit 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.

Therefore, the confirmation of the addition of this hill to Double Sub-Twmpau status is due to LIDAR analysis, resulting in a 26.8m summit height and as this hill is an island, this value also gives it 26.8m of drop, which is sufficient for it to be classified as a Double Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Garn Fawr 

Name:  Pig Stone 

OS 1:50,000 map:  157

Summit Height:  26.8m (LIDAR) 

Summit Grid Reference:  SM 71302 09244 (LIDAR)               

Bwlch Height:  N/A (sea level) 

Bwlch Grid Reference:  N/A (sea level) 

Drop:  26.8m (LIDAR) 

 

Myrddyn Phillips (October 2025) 

Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

Trwyn y Tal (SH 366 471) – 30-99m Sub-Twmpau addition (144th reclassification)

Summit Relocations post for Trwyn y Tal

 

There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Trwyn y Tal (SH 366 471)

The criteria for the list that this addition applies to are:

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Trwyn y Tal, and it is adjoined to the Yr Eifl group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with minor roads to its south-east, and the B4417 road farther to its south and the A499 road farther to its east, and has the small community of Trefor towards the south-east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 24m of drop, based on an estimated c 52m summit height and an estimated c 28m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

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

Therefore, the confirmation of the addition of this hill to 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 51.8m summit height and a 25.6m bwlch height, with these values giving this hill 26.2m of drop, which is sufficient for it to be classified as a 30-99m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Yr Eifl 

Name:  Trwyn y Tal 

OS 1:50,000 map:  123

Summit Height:  51.8m (LIDAR) 

Summit Grid Reference:  SH 36684 47142 & SH 36685 47143 (LIDAR)               

Bwlch Height:  25.6m (LIDAR) 

Bwlch Grid Reference:  SH 36604 46908 (LIDAR) 

Drop:  26.2m (LIDAR) 

 

Myrddyn Phillips (September 2025)

Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

Penpontbren Mochno (SN 630 925) – Double Sub-Twmpau addition (143rd reclassification) 

Significant Name Changes post for Penpontbren Mochno

 

There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Penpontbren Mochno (SN 630 925)

The criteria for the list that this addition applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Penpontbren Mochno and this was derived from the Tithe map, and it is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with the B4353 road to its north and west, and the A487 road to its east, and has the small community of Borth towards the south south-west.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 24m of drop, based on the 26m 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 the 2m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

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

Therefore, the confirmation of the addition of this hill to Double Sub-Twmpau status is due to LIDAR analysis, resulting in a 26.9m summit height and a 2.0m bwlch height, with these values giving this hill 24.8m of drop, which is sufficient for it to be classified as a Double Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Banc Llechwedd Mawr 

Name:  Penpontbren Mochno 

OS 1:50,000 map:  135

Summit Height:  26.9m (LIDAR) 

Summit Grid Reference:  SN 63095 92547 (LIDAR)               

Bwlch Height:  2.0m (LIDAR) 

Bwlch Grid Reference:  SN 62775 92295 (LIDAR) 

Drop:  24.8m (LIDAR) 

 

Myrddyn Phillips (August 2025)

Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

Yr Ynys (SN 614 896) – Double Sub-Twmpau addition (142nd reclassification)

Significant Height Revisions post for Yr Ynys

Significant Name Changes post for Yr Ynys

 

There has been an addition to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Yr Ynys (SN 614 896)

The criteria for the list that this addition applies to are:

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Yr Ynys and this was derived from the Tithe map, and it is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road and the B4353 road to its west, and has the small community of Borth towards the south-west. 

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

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category, as with no contours on the Ordnance Survey 1:25,000 Explorer map it was difficult to know whether any hill of note existed.  However, although details for this list were initially taken from the 1:25,000 series of mapping the Ordnance Survey 1:50,000 Landranger map does have a 20m uppermost ring contour for this hill. 

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.

Another resource now available online is the interactive mapping hosted on the Welsh Government website and entitled the DataMapWales.  This mapping has 5m contours and its detail matches that produced from the OS Terrain 5 product, which compliments much of that produced from LIDAR, and for this hill it has a 24m summit spot height. 

Extract from the DataMapWales

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 addition of this hill to Double Sub-Twmpau status is due to LIDAR analysis, resulting in a 25.45m summit height and a 3.0m bwlch height, with these values giving this hill 22.4m of drop, which is sufficient for it to be classified as a Double Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Banc Llechwedd Mawr 

Name:  Yr Ynys 

OS 1:50,000 map:  135

Summit Height:  25.45m (LIDAR) 

Summit Grid Reference:  SN 61402 89639 (LIDAR)               

Bwlch Height:  3.0m (LIDAR) 

Bwlch Grid Reference:  SN 61317 89488 & SN 61319 89492 (LIDAR) 

Drop:  22.4m (LIDAR) 

 

Myrddyn Phillips (July 2025)

Mapping Mountains - Hill Reclassifications - 30-99m Twmpau

Llein (SN 629 876) – 30-99m Sub-Twmpau addition (141st reclassification)

Significant Name Changes post for Llein

 

There has been confirmation of an addition to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Llein (SN 629 876)

The criteria for the list that this addition applies to are:

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

30-99m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Llein, and this was derived from the Tithe map, and it is adjoined to the Banc Llechwedd Mawr group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north and south, the B4353 road to its west and the A487 road to its east, and has the small community of Y Borth towards the west north-west.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 21m of drop, based on the 76m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 55m bwlch height, based on interpolation of 10m contouring between 50m – 60m. 

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.

Therefore, the confirmation of the addition of this hill to 30-99m Sub-Twmpau status is due to LIDAR analysis, resulting in a 76.1m summit height and a 51.7m bwlch height, with these values giving this hill 24.5m of drop, which is sufficient for it to be classified as a 30-99m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Banc Llechwedd Mawr 

Name:  Llein 

OS 1:50,000 map:  135

Summit Height:  76.1m (LIDAR) 

Summit Grid Reference:  SN 62972 87653 (LIDAR)               

Bwlch Height:  51.7m (LIDAR) 

Bwlch Grid Reference:  SN 63402 87483 & SN 63405 87481 (LIDAR) 

Drop:  24.5m (LIDAR) 

 

Myrddyn Phillips (July 2025)