Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

 

        Y Trechol –The Dominant Hills of Wales – Significant Height Revisions

Y Trechol –The Dominant Hills of Wales are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height, accompanying the Dominant list is a sub list entitled The Lesser Dominant Hills of Wales with the criteria for this sub category being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list commenced publication on Mapping Mountains on 03.012.15 with its Introduction giving details to its compilation and criteria, with Change Registers also created for the Dominant and the Lesser Dominant category.

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

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Penllwyngwyn Mawr (SN 549 007) - 57th significant height revision

Summit Relocations post for Penllwyngwyn Mawr

Significant Name Changes post for Penllwyngwyn Mawr

 

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

LIDAR image of Penllwyngwyn Mawr (SN 549 007)

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

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

30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Penllwyngwyn Mawr and this was derived from the Tithe map, and it is adjoined to the Mynydd Sylen group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the B4297 road to its immediate north and to its south, and has the town of Llanelli towards the west.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 72m summit height, based on the spot height positioned at SN 55146 00863 that appears on the contemporary Ordnance Survey 1:25,000 Explorer map. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 47m of drop, based on an estimated c 75m summit height positioned at SH 54904 00700 and an estimated c 28m bwlch height, based on interpolation of 5m contouring between 25m – 30m.  With the caveat that the uppermost 75m ring contour had been missed when the details for this hill were first compiled and published.

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 Penllwyngwyn Mawr (SN 549 007)

The summit height produced by LIDAR analysis is 76.8m and is positioned at SN 54907 00706, 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 76.8m and this was derived from LIDAR analysis, this is 4.8m higher than the originally listed summit height of 72m, 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 Sylen 

Name:  Penllwyngwyn Mawr 

OS 1:50,000 map:  164, 178

Summit Height (New Height):  76.8m (LIDAR) 

Summit Grid Reference:  SN 54907 00706 (LIDAR)               

Bwlch Height:  25.0m (LIDAR) 

Bwlch Grid Reference:  SN 53996 01771 (LIDAR) 

Drop:  51.8m (LIDAR) 

Dominance:  67.44% (LIDAR)

 

Myrddyn Phillips (October 2024)

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Cefn (SH 721 004) - 56th significant height revision

Hill Reclassifications post for Cefn

Significant Name Changes post for Cefn

 

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

LIDAR image of Cefn (SH 721 004)

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

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

100m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

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

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

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

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

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

LIDAR summit image of Cefn (SH 721 004)

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

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

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

 

The full details for the hill are:

Group:  Tarren y Gesail 

Name:  Cefn 

OS 1:50,000 map:  135

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

Summit Grid Reference:  SH 72126 00402 (LIDAR) 

Bwlch Height:  59.0m (LIDAR) 

Bwlch Grid Reference:  SH 72569 00795 (LIDAR) 

Drop:  59.2m (LIDAR) 

Dominance:  50.08% (LIDAR) 

 

Myrddyn Phillips (October 2024)

 

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Safle Claddu Nant y Caws (SN 468 174) & (SN 469 174) and Cae Mawr (SN 462 175) - 55th significant height revision

Hill Reclassifications post for Safle Claddu Nant y Caws (SN 468 174) & (SN 469 174) and Cae Mawr (SN 462 175) 

Summit Relocations post for Safle Claddu Nant y Caws (SN 468 174) & (SN 469 174) and Cae Mawr (SN 462 175)

  

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

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

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

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

100m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

Dual Summit hills:

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

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

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

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

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

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

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

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

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

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

 

The full details for the hill are:

Group:  Mynydd Sylen

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

OS 1:50,000 map:  159

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

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

Bwlch Height:  98.5m (LIDAR)

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

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

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

 

Myrddyn Phillips (July 2024)

  

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Cefn y Coed (SH 667 172) - 54th significant height revision

Summit Relocations post for Cefn y Coed

Significant Name Changes post for Cefn y Coed

 

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

LIDAR image of Cefn y Coed (SH 667 172)

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

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

30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

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

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a non-interpolated summit height of c 90m positioned at SH 666 172, with an accompanying note stating; Two points of same height, a reference to the two uppermost 90m ring contours that appear on the contemporary Ordnance Survey 1:25,000 Explorer map. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 64m of drop, based on an estimated c 91m summit height positioned at SH 66668 17206 and an estimated c 27m bwlch height, based on interpolation of 10m contouring between 20m – 30m, with these values giving this hill 70.33% dominance.

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

The summit height produced by LIDAR analysis is 89.0m and is positioned at SH 66751 17241, 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 89.0m and this was derived from LIDAR analysis, this is 2.0m lower than the previously listed summit height of c 90m, which was based on interpolation of the uppermost 90m ring contour that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Cadair Idris 

Name:  Cefn y Coed 

OS 1:50,000 map:  124

Summit Height (New Height):  89.0m (LIDAR) 

Summit Grid Reference:  SH 66751 17241 (LIDAR)               

Bwlch Height:  26.7m (LIDAR) 

Bwlch Grid Reference:  SH 67045 17182 (LIDAR) 

Drop:  62.3m (LIDAR) 

Dominance:  69.98% (LIDAR) 

 

Myrddyn Phillips (May 2024)

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Rhos Ymryson (SN 460 499) - 53rd significant height revision

Summit Relocations post for Rhos Ymryson

 

There has been a Significant Height Revision to a hill that is listed in the Y Trichant – The 300m Hills of Wales and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Rhos Ymryson (SN 460 499)

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

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales 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 Rhos Ymryson, 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 the B4338 road to its north-east, a minor road to its north-west and the A475 road to its south, and has the village of Llanwenog towards the south-east. 

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

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

When the original 300m 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 327m summit height, based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map and which is positioned at SN 459 500.  However, this height is given to the top of a covered reservoir, whilst the contemporary Ordnance Survey 1:50,000 Landranger map gives a 324m summit spot height, which conforms with the rounded up 1062ft (323.7m) height shown on the Ordnance Surveys series of Six-Inch maps. 

Extract from the Ordnance Survey series of Six-Inch maps

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 Rhos Ymryson (SN 460 499)

The summit height produced by LIDAR analysis to the highest remaining natural ground on this hill is 323.3m and is positioned at SN 46032 49996, 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 323.3m and this was derived from LIDAR analysis, this is 3.7m lower than the originally listed summit height of 327m, 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 Bach 

Name:  Rhos Ymryson 

OS 1:50,000 map:  146

Summit Height (New Height):  323.3m (LIDAR)                                                           

Summit Grid Reference:  SN 46032 49996 (LIDAR) 

Bwlch Height:  162.6m (LIDAR) 

Bwlch Grid Reference:  SN 61745 57992 (LIDAR) 

Drop:  160.8m (LIDAR) 

Dominance:  49.72% (LIDAR) 

 

Myrddyn Phillips (December 2023)

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Bolton Beacon (SM 917 112) - 52nd significant height revision

Significant Name Changes post for Bolton Beacon

 

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

LIDAR image of Bolton Beacon (SM 917 112)

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

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

The 100m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

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

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

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

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

LIDAR summit image of Bolton Beacon (SM 917 112)

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

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

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

 

The full details for the hill are: 

Group:  Garn Fawr 

Name:  Bolton Beacon 

OS 1:50,000 map:  157, 158

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

Summit Grid Reference:  SM 91710 11288 (LIDAR) 

Bwlch Height:  66.8m (LIDAR) 

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

Drop:  46.7m (LIDAR) 

Dominance:  41.13% (LIDAR) 

 

Myrddyn Phillips (September 2023)

 

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Needle Rock (SM 975 379) - 51st significant height revision

 

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

LIDAR image of Needle Rock (SM 975 379)

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

The 30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Needle Rock, and it is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with the A487 road to its south, and has the town of Abergwaun (Fishguard) towards the west south-west.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a summit height of 40m, with an accompanying note stating; Approximate height of tidal sea stack from Dave Viggers. 

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

This hill is a sea stack and is cut off from mainland Wales at high tide.  As the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map give this hill no spot height or contours 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 Needle Rock (SM 975 379)

The summit height produced by LIDAR analysis is 33.9m and is positioned at SM 97569 37997, 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 33.9m and this was derived from LIDAR analysis, this is 6.1m lower than the originally listed summit height of 40m, which was based on an approximation given the author by Dave Viggers.

 

The full details for the hill are:

Group:  Mynydd Preseli 

Name:  Needle Rock 

OS 1:50,000 map:  159

Summit Height (New Height):  33.9m (LIDAR) 

Summit Grid Reference:  SM 97569 37997 (LIDAR)               

Bwlch Height:  N/A sea level (LIDAR) 

Bwlch Grid Reference:  SM 97566 37987 (LIDAR) 

Drop:  33.9m (LIDAR) 

Dominance:  100.00% (LIDAR) 

 

Myrddyn Phillips (August 2023)

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Morris’ Meadow (SN 019 183) - 50th significant height revision

Summit Relocations post for Morris' Meadow

Significant Name Changes post for Morris' Meadow

 

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

LIDAR image of Morris' Meadow (SN 019 183)

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

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

The 100m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

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

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

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

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

LIDAR summit image of Morris Meadow (SN 019 183)

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

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

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

 

The full details for the hill are: 

Group:  Mynydd Preseli 

Name:  Morris’ Meadow 

OS 1:50,000 map:  157, 158

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

Summit Grid Reference:  SN 01923 18373 (LIDAR) 

Bwlch Height:  65.2m (LIDAR) 

Bwlch Grid Reference:  SN 01619 20933 (LIDAR) 

Drop:  54.2m (LIDAR) 

Dominance:  45.41% (LIDAR) 

 

Myrddyn Phillips (May 2023)

 

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Pen y Ddinas (SN 627 357) - 49th significant height revision

Hill Reclassifications post for Pen y Ddinas

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 - Y Trechol - The Dominant Hills of Wales

Lan Ddu Cilwenau (SN 572 371) - 48th significant height revision

Summit Relocations post for Lan Ddu Cilwenau

Significant Name Changes post for Lan Ddu Cilwenau

 

There has been a Significant Height Revision to a hill that is listed in the Y Trichant – The 300m Hills of Wales and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data and LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Lan Ddu Cilwenau (SN 572 371)

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

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales 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 Lan Ddu Cilwenau, 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 B4337 road to its north-east, a minor road to its south-west and the B4310 road to its south-east, and has the village of Llansawel towards the east south-east.

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a summit height of 328m, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

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

LIDAR summit image of Lan Ddu Cilwenau (SN 572 371)

The summit height produced by LIDAR analysis is 333.1m and is positioned at SN 57277 37147, 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 333.1m and this was derived from LIDAR analysis, this is 5.1m higher than the previously listed summit height of 328m, which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Mynydd Pencarreg 

Name:  Lan Ddu Cilwenau 

OS 1:50,000 map:  146

Summit Height (New Height):  333.1m (LIDAR) 

Summit Grid Reference:  SN 57277 37147 (LIDAR) 

Bwlch Height:  c 211m (interpolation) 

Bwlch Grid Reference:  SN 56467 37617 (interpolation) 

Drop:  c 122m (LIDAR summit and interpolated bwlch) 

Dominance:  36.66% (LIDAR summit and interpolated bwlch) 

 

Myrddyn Phillips (May 2022)

 

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Cae Cwarre (SN 506 209) - 47th significant height revision

Hill Reclassifications post for Cae Cwarre

Significant Name Changes post for Cae Cwarre

 

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

LIDAR image of Cae Cwarre (SN 506 209)

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

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

The 30-99m Twmpau by Myrrdyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Cae Cwarre and this was derived from the Tithe map, and it is adjoined to the Mynydd Mallaen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with the A40 road to its north, a minor road to its west and the B4300 road to its south, and has the small community of Llanegwad towards the east north-east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a summit height of 68m based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 34m of drop, based on the 68m summit spot height and an estimated c 34m bwlch height, based on interpolation of 10m contouring between 30m – 40m, with these values giving this hill 50% dominance. 

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

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and for this hill it had 5m contouring, resulting in the bwlch height being amended to an estimated c 37m based on interpolation of contours between 35m – 40m, resulting in this hill being listed with an estimated c 31m of drop and 45.59% dominance.

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

LIDAR summit image of Cae Cwarre (SN 506 209)

The summit height produced by LIDAR analysis is 70.9m and is positioned at SN 50644 20918, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 70.9m and this was derived from LIDAR analysis, this is 2.9m higher than the previously listed summit height of 68m, which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Mynydd Mallaen 

Name:  Cae Cwarre 

OS 1:50,000 map:  159

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

Summit Grid Reference:  SN 50644 20918 (LIDAR)               

Bwlch Height:  36.1m (LIDAR) 

Bwlch Grid Reference:  SN 51854 21860 (LIDAR) 

Drop:  34.8m (LIDAR) 

Dominance:  49.04% (LIDAR) 

 

Myrddyn Phillips (May 2022)

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Castell y Dryslwyn (SN 554 203) - 46th significant height revision

Significant Name Changes post for Castell y Dryslwyn

 

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

LIDAR image of Castell y Dryslwyn (SN 554 203)

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

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

The 30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

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

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a summit height of 71m based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger map. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 50m of drop, based on an estimated c 76m summit height based on interpolation of the uppermost 75m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map, and an estimated c 26m bwlch height based on interpolation of 5m contouring between 25m – 30m. 

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

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

LIDAR summit image of Castell y Dryslwyn (SN 554 203)

The summit height produced by LIDAR analysis is 72.4m and is positioned at SN 55420 20301, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

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

 

The full details for the hill are:

Group:  Mynydd Mallaen 

Name:  Castell y Dryslwyn 

OS 1:50,000 map:  159

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

Summit Grid Reference:  SN 55420 20301 (LIDAR)               

Bwlch Height:  25.3m (LIDAR) 

Bwlch Grid Reference:  SN 55696 20577 (LIDAR) 

Drop:  47.1m (LIDAR) 

Dominance:  65.02% (LIDAR) 

 

Myrddyn Phillips (May 2022)

 

 

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Allt Dan Tŷ Mawr (SN 520 228) - 45th significant height revision

Hill Reclassifications post for Allt Dan Tŷ Mawr

  

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

LIDAR image of Allt Dan Tŷ Mawr (SN 520 228)

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

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

The 30m-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

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

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 29m of drop, based on an estimated c 67m summit height and the 38m bwlch spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and for this hill it had a 69m summit spot height positioned at SN 51824 22804, and when coupled with the 38m bwlch spot height these values gave this hill 31m of drop and 44.93% dominance.

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

LIDAR summit image of Allt Dan Tŷ Mawr (SN 520 228)

The summit height produced by LIDAR analysis is 72.65m and is positioned at SN 52004 22867, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 72.65m and this was derived from LIDAR analysis, this is 3.65m higher than the previously listed summit height of 69m, which was based on the spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and 5.65m higher than its originally listed interpolated height of c 67m.

 

The full details for the hill are:

Group:  Mynydd Mallaen 

Name:  Allt Dan Tŷ Mawr 

OS 1:50,000 map:  159

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

Summit Grid Reference:  SN 52004 22867 (LIDAR)               

Bwlch Height:  39.0m (LIDAR) 

Bwlch Grid Reference:  SN 52223 22857 (LIDAR) 

Drop:  33.7m (LIDAR) 

Dominance:  46.32% (LIDAR)

 

Myrddyn Phillips (May 2022)

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Pen Lan Fawr (SN 626 222) - 44th significant height revision

Hill Reclassifications post for Pen Lan Fawr

 

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

LIDAR image of Pen Lan Fawr (SN 626 222)

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

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

The 30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Pen Lan Fawr and it is adjoined to the Mynydd Mallaen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north, the Afon Tywi to its south and the A483 road to its east, and has the town of Llandeilo towards the north-east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a 95m summit height, based on the spot height that is positioned at SN 62616 22258 and appears on the Ordnance Survey 1:25,000 Explorer map. 

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

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

LIDAR summit image of Pen Lan Fawr (SN 626 222)

The summit height produced by LIDAR analysis is 98.3m and is positioned at SN 62626 22229, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 98.3m and this was derived from LIDAR analysis, this is 3.3m higher than the originally listed summit height of 95m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Mynydd Mallaen 

Name:  Pen Lan Fawr 

OS 1:50,000 map:  159

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

Summit Grid Reference:  SN 62626 22229 (LIDAR)               

Bwlch Height:  64.9m (LIDAR) 

Bwlch Grid Reference:  SN 61761 22561 (LIDAR) 

Drop:  33.4m (LIDAR) 

Dominance:  33.97% 

 

Myrddyn Phillips (May 2022)

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Y Grongaer (SN 573 215 and SN 574 215) - 43rd significant height revision

Summit Relocations post for Y Grongaer

 

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

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

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

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

The 100m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

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

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

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

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

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

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

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

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

 

The full details for the hill are:

Group:  Mynydd Mallaen 

Name:  Y Grongaer 

OS 1:50,000 map:  159

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

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

Bwlch Height:  53.05m (LIDAR) 

Bwlch Grid Reference:  SN 57923 22123 (LIDAR) 

Drop:  87.6m (LIDAR) 

Dominance:  62.29% (LIDAR) 

 

Myrddyn Phillips (April 2022)

 

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Fan (SN 672 315) - 42nd 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 - Y Trechol - The Dominant Hills of Wales

Cefn Coch (SH 610 396) - 41st significant height revision

Survey post for Cefn Coch

Significant Name Changes post for Cefn Coch

 

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

LIDAR image of Cefn Coch (SH 610 396)

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

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

The 30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Cefn Coch and it is adjoined to the Moelwynion group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A498 road and the B4410 road to its north-west, the A497 road and the A487 road to its south-west and the A4085 road to its east, and has the town of Penrhyndeudraeth towards the south. 

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the P30 category, and it was listed with an 81m summit height, with an accompanying note stating; 86m on 1984 1:50,000 map. 

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 33m of drop and 40.74% dominance, based on the 81m summit spot height and the 48m bwlch spot height that appear on the Ordnance Survey 1:25,000 Explorer map. 

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

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

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

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

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

LIDAR summit image of Cefn Coch (SH 610 396)

The summit height produced by LIDAR analysis is 86.6m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

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

 

The full details for the hill are:

Group:  Moelwynion 

Name:  Cefn Coch 

OS 1:50,000 map:  124

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

Summit Grid Reference:  SH 61030 39620 (LIDAR)               

Bwlch Height:  51.5m (LIDAR) 

Bwlch Grid Reference:  SH 61461 39763 (LIDAR) 

Drop:  35.1m (LIDAR) 

Dominance:  40.51% (LIDAR) 

 

Myrddyn Phillips (December 2021)

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Ynys Dafydd (SH 646 174) - 40th significant height revision

Hill Reclassifications post for Ynys Dafydd

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill obtained from the summit analysis programme using LIDAR produced by Joe Nuttall, and then by LIDAR analysis initially conducted by Jim Bloomer and subsequently by Myrddyn Phillips. 

LIDAR image of Ynys Dafydd (SH 646 174)

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

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

The 30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Ynys Dafydd, and it is adjoined to the Rhinogydd group of hills, which are situated in the western part of North Wales (Region A, Sub-Region A3), and it is positioned with the coast to its south-west, the Afon Dyfi (River Dovey) to its south and the A496 road to its north-west, and has the town of Abermaw (Barmouth) towards the west south-west. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 27m of drop based on an estimated c 42m summit height and an estimated c 15m bwlch height, with both values based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map, with 40m being the uppermost contour given the hill on this map. 

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

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

LIDAR summit image of Ynys Dafydd

The summit height produced by LIDAR analysis is 52.8m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

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

 

The full details for the hill are:

Group:  Rhinogydd 

Name:  Ynys Dafydd 

OS 1:50,000 map:  124

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

Summit Grid Reference:  SN 64636 17484 (LIDAR) 

Bwlch Height:  17.1m (LIDAR) 

Bwlch Grid Reference:  SN 64599 17744 (LIDAR) 

Drop:  35.7m (LIDAR) 

Dominance:  67.61% (LIDAR)

 

Myrddyn Phillips (September 2021)

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Ynys Hir (SN 679 957) - 39th significant height revision

 

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill derived by Joe Nuttall who produced a summit analysis programme using LIDAR, and then by LIDAR analysis initially conducted by Chris Crocker and subsequently by Myrddyn Phillips. 

LIDAR image of Ynys Hir (SN 679 957)

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

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

The 30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Ynys Hir, and it is adjoined to the Pumlumon group of hills which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the Afon Dyfi (River Dovey) and the coast to its west and has the A487 road to its east and the village of Y Borth towards the south-west. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 41m of drop, based on an estimated c 48m summit height and an estimated c 7m bwlch height, with both values based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map, with 40m being the uppermost contour given the hill on this map. 

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

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

The summit height produced by LIDAR analysis is 61.1m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

Therefore, this hill’s new listed summit height is 61.1m and this was derived from LIDAR analysis, this is 13.1m higher than the previous listed summit height of c 48m which was derived from interpolation of the uppermost contour given the hill on contemporary Ordnance Survey 1:25,000 Explorer maps.

 

The full details for the hill are:

Group:  Pumlumon 

Name:  Ynys Fach 

OS 1:50,000 map:  135

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

Summit Grid Reference:  SN 67972 95798 (LIDAR) 

Bwlch Height:  6.8m (LIDAR) 

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

Drop:  54.35m (LIDAR) 

Dominance:  88.91% (LIDAR)

 

Myrddyn Phillips (August 2021)

 

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

The Park (SN 664 936) - 38th significant height revision

Hill Reclassifications post for The Park

 

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

LIDAR image of The Park (SN 664 936)

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

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

The 30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is The Park, and it is adjoined to the Pumlumon group of hills which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the Afon Dyfi to its north, the coast to its west and the A487 road to its east, and has the village of Tal-y-bont towards the south. 

When the original 30-99m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website were standardised and interpolated heights and drop values also included the details for this hill were re-evaluated, and it was listed with an estimated c 41m drop and 49.40% dominance, based on an estimated c 83m summit height and the 42m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

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

LIDAR summit image of The Park (SN 664 936)

The summit height produced by LIDAR analysis is 85.6m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

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

 

The full details for the hill are:

Group:  Pumlumon 

Name:  The Park 

OS 1:50,000 map:  135

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

Summit Grid Reference:  SN 66441 93678 (LIDAR)

Bwlch Height:  42.7m (LIDAR)

Bwlch Grid Reference:  SN 66477 93308 (LIDAR)

Drop:  42.9m (LIDAR)

Dominance:  50.09% (LIDAR)

 

Myrddyn Phillips (August 2021)

 

 

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Ynys Cynfelyn (SN 649 919) - 37th significant height revision

Significant Name Changes post for Ynys Cynfelyn

 

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

LIDAR image of Ynys Cynfelyn (SH 649 919)

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

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

The 30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Ynys Cynfelyn, and it is adjoined to the Pumlumon group of hills which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the coast to its west, the B4353 road to its north, a minor road to its south and the A487 road to its east, and has the village of Tal-y-bont towards the south. 

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 36m of drop based on an estimated c 43m summit height and an estimated c 7m bwlch height, with both values based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

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

LIDAR summit image of Ynys Cynfelyn (SH 649 919)

The summit height produced by LIDAR analysis is 45.1m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

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

 

The full details for the hill are:

Group:  Pumlumon 

Name:  Ynys Cynfelyn 

OS 1:50,000 map:  135

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

Summit Grid Reference:  SN 64923 91967 (LIDAR) 

Bwlch Height:  5.5m (LIDAR) 

Bwlch Grid Reference:  SN 65441 92012 (LIDAR) 

Drop:  39.65m (LIDAR) 

Dominance:  87.88% (LIDAR) 

 

Myrddyn Phillips (July 2021)

 

 

Mapping Mountains - Significant Height Revisions - Y Trechol - The Dominant Hills of Wales

Castell (SN 585 789) - 36th significant height revision

Survey post for Castell

Significant Name Changes post for Castell

 

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

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

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

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

The 30-99m Twmpau by Myrddyn Phillips

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Castell and it is adjoined to the Elenydd group of hills which are situated in the central part of the Mid and West Wales Region (Region B, Sub-Region B2), and it is positioned with the coast to its west, the Afon Ystwyth to its east and the A487 road farther to its east, and has the town of Aberystwyth towards the north. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 29m of drop, based on the 73m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 44m bwlch height based on interpolation of 10m contouring between 40m – 50m. 

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

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

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

LIDAR image of Castell

The summit height produced by LIDAR analysis is 77.4m, and as the summit has now been surveyed with the Trimble GeoXH 6000 giving 77.2m it is this result that is being prioritised for listing purposes, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are: 

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

Therefore, this hill’s new listed summit height is 77.2m and this was derived from a Trimble GeoXH 6000 survey, this is 4.2m higher than the previous listed summit height of 73m which was based on the spot height that appears on contemporary Ordnance Survey 1:25,000 Explorer maps.

 

The full details for the hill are:

Group:  Elenydd 

Name:  Castell 

OS 1:50,000 map:  135

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

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

Bwlch Height:  42.3m (LIDAR) 

Bwlch Grid Reference:  SN 58197 78954 (LIDAR) 

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

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

 

Myrddyn Phillips (April 2021)