Y Trechol –The Dominant Hills of Wales – Significant Height Revisions
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) |
Y Trichant - The 300m Hills of Wales by Myrddyn Phillips |
Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
Extract from the Ordnance Survey 1:50,000 Landranger map |
Extract from the Ordnance Survey series of Six-Inch maps |
LIDAR summit image of Rhos Ymryson (SN 460 499) |
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 100m Twmpau by Myrddyn Phillips |
Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Bolton Beacon (SM 917 112) |
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 by Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
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 100m Twmpau by Myrddyn Phillips |
Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Morris Meadow (SN 019 183) |
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 200m Twmpau by Myrddyn Phillips |
Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Pen y Ddinas (SN 627 357) |
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) |
Y Trichant - The 300m Hills of Wales by Myrddyn Phillips |
Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Lan Ddu Cilwenau (SN 572 371) |
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 30-99m Twmpau by Myrrdyn Phillips |
Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Cae Cwarre (SN 506 209) |
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 30-99m Twmpau by Myrddyn Phillips |
Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips |
Extract from the Ordnance Survey 1:50,000 Landranger map |
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Castell y Dryslwyn (SN 554 203) |
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 TÅ· Mawr (SN 520 228) - 45th significant height revision
Hill Reclassifications post for Allt Dan TÅ· 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 TÅ· Mawr (SN 520 228) |
The 30m-99m Twmpau by Myrddyn Phillips |
Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Allt Dan TÅ· Mawr (SN 520 228) |
The full details for the hill are:
Group: Mynydd Mallaen
Name: Allt Dan TÅ· 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 30-99m Twmpau by Myrddyn Phillips |
Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Pen Lan Fawr (SN 626 222) |
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) |
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 by Myrddyn Phillips |
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Y Grongaer (SN 573 215 and SN 574 215) |
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) |
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 by Myrddyn Phillips |
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 |
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 |
LIDAR summit image of Fan (SN 672 315) |
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
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) |
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 by Myrddyn Phillips |
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 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 |
LIDAR summit image of Cefn Coch (SH 610 396) |
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) |
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 by Myrddyn Phillips |
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 |
LIDAR summit image of Ynys Dafydd |
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) |
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 by Myrddyn Phillips |
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 |
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) |
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 by Myrddyn Phillips |
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 |
LIDAR summit image of The Park (SN 664 936) |
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) |
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 by Myrddyn Phillips |
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 |
LIDAR summit image of Ynys Cynfelyn (SH 649 919) |
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)
Castell (SN 585 789) - 36th significant height revision
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) |
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 by Myrddyn Phillips |
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 |
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 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)
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