Myrddyn Phillips - Mapping Mountains: Mapping Mountains – Significant Height Revisions

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

Ynys Fach (SN 668 951) - 35th significant height revision

Hill Reclassifications post for Ynys Fach

Summit Relocations post for Ynys Fach

Significant Name Changes post for Ynys Fach

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 Jim Bloomer and subsequently by Myrddyn Phillips.

LIDAR image of Ynys Fach (SN 668 951)

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 Ynys Fach, 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 has the A487 road to its south-east and the town of Machynlleth 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 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.

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 27m of drop based on an estimated c 34m 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 30m 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 Fach

The summit height produced by LIDAR analysis is 43.5m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 43.5m and this was derived from LIDAR analysis, this is 9.5m higher than the previous listed summit height of c 34m 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): 43.5m (LIDAR)

Summit Grid Reference: SN 66845 95141 (LIDAR)

Bwlch Height: 2.1m (LIDAR)

Bwlch Grid Reference: SN 67483 95096 (LIDAR)

Drop: 41.3m (LIDAR)

Dominance: 95.10% (LIDAR)

Myrddyn Phillips (April 2021)

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

The Larches (ST 433 899) - 34th significant height revision

Significant Name Changes post for The Larches

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 The Larches (ST 433 899)

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

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 The Larches, and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with minor roads to its north, west, south and east and further afield has the A48 road to its north and the M4 motorway to its south, and has the city of Casnewydd (Newport) towards the west.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a c 85m summit height, this being the uppermost contour that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at ST 433 899.

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

When this list was standardised, and interpolated heights and drop values also included the details for this hill was re-assessed and it was listed with an estimated c 89m summit height based on interpolation of 5m contouring that appears on the Ordnance Survey 1:25,000 Explorer map.

LIDAR summit image of The Larches

The summit height produced by LIDAR analysis is 91.1m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 91.1m and this was derived from LIDAR analysis, this is 2.1m higher than the previous listed summit height of c 89m and 6.1m higher than the uppermost 85m ring contour on contemporary Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Group: Gwent Is Coed

Name: The Larches

OS 1:50,000 map: 171, 172

Summit Height (New Height): 91.1m (LIDAR)

Summit Grid Reference: ST 43303 89957 (LIDAR)

Bwlch Height: 22.3m (LIDAR)

Bwlch Grid Reference: ST 42928 90248 (LIDAR)

Drop: 68.8m (LIDAR)

Dominance: 75.54% (LIDAR)

Myrddyn Phillips (September 2020)

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

Waltwood Hill (ST 386 885) - 33rd significant height revision

Summit Relocations post for Waltwood Hill

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 Waltwood Hill (ST 386 885)

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

The name the hill is listed by is Waltwood Hill, and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the M4 motorway to its north, the A48 road to its west and the A4810 road to its south, and has the city of Casnewydd (Newport) towards the west.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 68m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and which is positioned at ST 38637 88605.

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

LIDAR summit image of Waltwood Hill

The summit height produced by LIDAR analysis is 70.2m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 70.2m and this was derived from LIDAR analysis, this is 2.2m higher than the previous listed summit height of 68m that appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Gwent Is Coed

Name: Waltwood Hill

OS 1:50,000 map: 171

Summit Height (New Height): 70.2m (LIDAR)

Summit Grid Reference: ST 38646 88595 (LIDAR)

Bwlch Height: 21.7m (LIDAR)

Bwlch Grid Reference: ST 39426 89069 and ST 39433 89070 (LIDAR)

Drop: 48.5m (LIDAR)

Dominance: 69.07% (LIDAR)

Myrddyn Phillips (August 2020)

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

The Knoll (ST 424 904) - 32nd significant height revision

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 confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of The Knoll (ST 424 904)

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 with 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.

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

The name the hill is listed by is The Knoll, and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the A48 road to its north and the M4 motorway to its south, and has the city of Casnewydd (Newport) 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 c 90m summit height, based on its uppermost contour 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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with c 51m of drop, based on an estimated c 94m summit height based on interpolation of 5m contouring and a 43m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

LIDAR close up image of The Knoll

The summit height produced by LIDAR analysis is 101.9m positioned at ST 42467 90424, this is a substantial height revision compared to some revised heights and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, this hill’s new listed summit height is 101.9m and this was produced by LIDAR analysis, this is 7.9m higher than its previously listed height of c 94m which was based on interpolation of its uppermost 90m ring contour on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Gwent Is Coed

Name: The Knoll

OS 1:50,000 map: 171, 172

Summit Height (New Height): 101.9m (LIDAR)

Summit Grid Reference: ST 42467 90424 (LIDAR)

Bwlch Height: 43.1m (LIDAR)

Bwlch Grid Reference: ST 42135 90345 (LIDAR)

Drop: 58.7m (LIDAR)

Dominance: 57.66% (LIDAR)

Myrddyn Phillips (July 2020)

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

Chepstow Hill (ST 355 905) - 31st significant height revision

Summit Relocations post for Chepstow Hill

LIDAR image of Chepstow Hill (ST 355 905)

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

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

The name the hill is listed by is Chepstow Hill and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Wysg (River Usk) to its north-west, the M4 motorway to its south and the A449 road to its east, and has the city of Casnewydd (Newport) towards the 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 111m summit height based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online. This mapping had many spot heights not on other publicly available Ordnance Survey maps and gives a 114m spot height on the summit area of this hill and positioned at ST 356 905. This 114m spot height also appears on Ordnance Survey data available on the Magic Maps website.

Extract from the Magic Maps website

The summit height produced by LIDAR analysis is 116.6m positioned at ST 35547 90567, this is a substantial height revision compared to the original 111m listed summit height, and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 116.6m and this was produced by LIDAR analysis, this is 5.6m higher than its original listed height of 111m that appears as a spot height on the Ordnance Survey 1:25,000 Explorer map, and 2.6m higher than that of the online Vector Map Local.

The full details for the hill are:

Group: Gwent Is Coed

Name: Chepstow Hill

OS 1:50,000 map: 171

Summit Height (New Height): 116.6m (LIDAR)

Summit Grid Reference: ST 35547 90567 (LIDAR)

Bwlch Height: 63.2m (LIDAR)

Bwlch Grid Reference: ST 36979 90843 (LIDAR)

Drop: 53.4m (LIDAR)

Dominance: 45.76% (LIDAR)

Myrddyn Phillips (June 2020)

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

Mynydd Llwyd (ST 433 935) - 30th significant height revision

Significant Name Changes post for Mynydd Llwyd

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height, their locations, the drop, dominance and status of the hill derived from detail on contemporary and historic Ordnance Survey maps.

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

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

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

The name the hill is listed by is Mynydd Llwyd and it is adjoined to the Gwent Is Coed group of hills which are situated in the south-eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the A449 road to its west, the A48 road to its south and the B4235 road to its north-east, and has the city of Casnewydd (Newport) towards the west south-west.

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

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the main P30 list under the name of Gray Hill and listed with a 273m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating; 275m on 1986 1:50000 map.

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

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

Extract from the Ordnance Survey series of Six-Inch maps

As the Surface Height is more accurate than the 273m spot height which has been ascertained from photogrammetry, the 275m height is now used for this hill, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

The full details for the hill are:

Group: Gwent Is Coed

Name: Mynydd Llwyd

OS 1:50,000 map: 171, 172

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

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

Bwlch Height: c 183m (interpolation)

Bwlch Grid Reference: ST 42894 93984 (interpolation)

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

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

Myrddyn Phillips (May 2020)

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

Coed Anghred Hill (SO 457 194) - 29th significant height revision

Summit Relocations post for Coed Anghred Hill

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 confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Coed Anghred Hill (SO 457 194)

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

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

The name the hill is listed by is Coed Anghred Hill and it is adjoined to the Mynyddoedd Duon group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with the Afon Mynwy (River Monnow) and the B4521 road to its north and the B4347 road to its west, and has the small village of Ynysgynwraidd (Skenfrith) towards the north.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 192m summit height based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SO 45823 19468.

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

LIDAR summit image of Coed Anghred Hill

The height produced by LIDAR analysis is 198.8m and is positioned at SO 45713 19487, this is a substantial revision compared to some revised heights, and comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 198.8m and this was derived from LIDAR analysis, this is 6.8m higher than the previously listed summit height of 192m which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group: Mynyddoedd Duon

Name: Coed Anghred Hill

OS 1:50,000 map: 161

Summit Height (New Height): 198.8m (LIDAR)

Summit Grid Reference: SO 45713 19487 (LIDAR)

Bwlch Height: 128.8m (LIDAR)

Bwlch Grid Reference: SO 44881 19181 (LIDAR)

Drop: 70.0m (LIDAR)

Dominance: 35.20%

Myrddyn Phillips (March 2020)

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

Coed y Bwnydd (SO 366 069) - 28th significant height revision

Hill Reclassifications post for Coed y Bwnydd

Significant Name Changes post for Coed y Bwnydd

Summit Relocations post for Coed y Bwnydd

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

LIDAR image of Coed y Bwnydd (SO 366 069)

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

200m Twmpau by Myrddyn Phillips

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

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

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

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

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

Extract from the Magic Maps website

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

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

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

The full details for the hill are:

Group: Mynyddoedd Duon

Name: Coed y Bwnydd

OS 1:50,000 map: 161

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

Summit Grid Reference: SO 36613 06919 (LIDAR)

Bwlch Height: 59.4m (LIDAR)

Bwlch Grid Reference: SO 39308 08901 (LIDAR)

Drop: 142.0m (LIDAR)

Dominance: 70.50%

Myrddyn Phillips (February 2020)

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

Dinas Powys (ST 148 722) - 27th significant height revision

Hill Reclassifications post for Dinas Powys

There has been a Significant Height Revision to a hill that is now 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 Dinas Powys (ST 148 722)

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

The name the hill is listed by is Dinas Powys and it is adjoined to the Bro Morgannwg group of hills, which are situated in the southern part of South Wales (Region C, Sub-Region C2), and it is encircled by a number of A roads, with the A4232 to its north, the A4050 to its west, the A4231 towards its south and the A4055 to its east, and has the town of Y Barri (Barry) to the south-west and the town of Penarth 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 that accompanied the main P30 list, as it did not meet the criteria then used in the main P30 list.

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 a c 62m interpolated summit height and the 33m spot height that appears at the bwlch on Ordnance Survey 1:25,000 Explorer maps which for this area has contours at 5m intervals.

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

The details for this hill were re-examined when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online. This mapping has many spot heights not on other publicly available Ordnance Survey maps.

Extract from the Ordnance Survey Vector Map Local

The details for this hill were also re-assessed when the OS Maps website became available online. This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and the online Vector Map Local. These re-assessments resulted in the hill being listed with c 30m of drop with the interpolated summit height increasing from c 62m to c 63m.

Extract from the OS Maps website

LIDAR summit image of Dinas Powis

The summit height produced by LIDAR analysis is 69.4m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 69.4m and this was derived from LIDAR analysis, this is 6.4m higher than the previous estimated summit height of c 63m and 9.4m higher than the uppermost 60m ring contour on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, but it is in accordance with the uppermost 65m ring contour on the OS Maps website.

The full details for the hill are:

Group: Bro Morgannwg

Name: Dinas Powys

OS 1:50,000 map: 171

Summit Height (New Height): 69.4m (LIDAR)

Summit Grid Reference: ST 14823 72225 (LIDAR)

Bwlch Height: 33.6m (LIDAR)

Bwlch Grid Reference: ST 14757 72333 (LIDAR)

Drop: 35.8m (LIDAR)

Dominance: 51.57% (LIDAR)

Myrddyn Phillips (November 2019)

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

Ash Tip (ST 031 663) - 26th significant height revision

Hill Reclassifications post for Ash Tip

Significant Name Changes post for Ash Tip

LIDAR image of Ash Tip (ST 031 663)

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.

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.

The name the hill is now listed by is Ash Tip and this was derived from local enquiry, and it is adjoined to the Bro Morgannwg group of hills, which are situated in the southern part of South Wales (Region C, Sub-Region C2), and it forms a part of landscaped ground that once made up the Aberthaw quarry and lime works, and it is positioned with the B4265 road to its north, and has the small community of Sain Tathan (St Athan) towards the north-west.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in either the main P30 list or the Hills to be surveyed sub list, as contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps of the day showed the area that now makes up this hill as having no ring contours of note.

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

This area was re-examined when the OS Maps website became available online. This is the replacement for OS Get-a-map and has contours at 5m intervals and for the majority of land comprising old mine workings it shows present day contours, as opposed to the blank space showed on the counterparts of the 1:50,000 Landranger and 1:25,000 Explorer maps.

Extract from the OS Maps website

The summit height produced by LIDAR analysis is 50.0m and as there are no contours of any significance on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 50.0m and this was derived from LIDAR analysis, this is 40m higher than the uppermost 10m ring contour on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Group: Bro Morgannwg

Name: Ash Tip

OS 1:50,000 map: 170

Summit Height (New Height): 50.0m (LIDAR)

Summit Grid Reference: ST 03170 66338 (LIDAR)

Bwlch Height: 12.4m (LIDAR)

Bwlch Grid Reference: ST 03298 66735 (LIDAR)

Drop: 37.6m (LIDAR)

Dominance: 75.20% (LIDAR)

Myrddyn Phillips (November 2019)

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

Wenvoe Quarry (ST 131 741) - 25th significant height revision

Significant Name Changes post for Wenvoe Quarry

Summit Relocations post for Wenvoe Quarry

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 and its position confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR summit image of Wenvoe Quarry (ST 131 741)

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 with 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 name the hill is now listed by is Wenvoe Quarry and it is adjoined to the Bro Morgannwg group of hills, which are situated in the southern part of South Wales (Region C, Sub-Region C2), and it is positioned with a number of A roads encircling it with the A4232 to its north and east, the A4050 to its west and the A4055 further to its south-east, and has the city of Caerdydd (Cardiff) towards the north-east.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a c 115m summit height, based on the uppermost contour on contemporary Ordnance Survey 1:25,000 Explorer maps.

When this 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 117m summit height based on interpolation of the uppermost 115m contour on the Ordnance Survey 1:25,000 Explorer map, with this summit height later being changed to an estimated c 118m.

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

The height produced by LIDAR analysis is 123.4m and is positioned at ST 13189 74189, this is a substantial revision compared to some revised heights, and comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 123.4m and this was derived from LIDAR analysis, this is 5.4m higher than the previously listed summit height of c 118m which was based on an estimated height from interpolation of its uppermost 115m contour on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Bro Morgannwg

Name: Wenvoe Quarry

OS 1:50,000 map: 171

Summit Height (New Height): 123.4m (LIDAR)

Summit Grid Reference: ST 13189 74189 (LIDAR)

Bwlch Height: 66m (spot height)

Bwlch Grid Reference: ST 12669 74393 (spot height)

Drop: 57m (LIDAR summit and spot height bwlch)

Dominance: 46.51% (LIDAR summit and spot height bwlch)

Myrddyn Phillips (October 2019)

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

Woodlake Park (ST 343 997) - 24th significant height revision

Significant Name Changes post for Woodlake Park

Summit Relocations post for Woodlake Park

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 and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Woodlake Park (AT 343 997)

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

The name the hill is listed by is Woodlake Park and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is positioned above the Llandegfedd Reservoir which is to its west, and has the town of Pont-y-pŵl (Pontypool) towards its west and Brynbuga (Usk) towards its east.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 147m summit height, based on the spot height positioned at ST 340 994 that appears on the Ordnance Survey 1:50,000 Landranger map, with the 1:25,000 Explorer map having no spot height.

The details for this hill were re-evaluated when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online, and as this map gives a 149m spot height positioned at ST 34341 99786, the summit of this hill was relocated.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

The height produced by LIDAR analysis is 150.7m positioned at ST 34335 99793, this is not a substantial revision compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 150.7m and this was derived from LIDAR analysis, this is 1.7m higher than the previously listed summit height of 149m which was derived from the spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website.

The full details for the hill are:

Group: Cymoedd Gwent

Name: Woodlake Park

OS 1:50,000 map: 171

Summit Height (New height): 150.7m (LIDAR)

Summit Grid Reference: ST 34335 99793 (LIDAR)

Bwlch Height: 91.5m (LIDAR)

Bwlch Grid Reference: ST 33405 01033 (LIDAR)

Drop: 59.3m (LIDAR)

Dominance: 39.31%

Myrddyn Phillips (August 2019)

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

The Mount (ST 258 848) - 23rd significant height revision

Significant Name Changes post for The Mount

Summit Relocations post for The Mount

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 derived from the OS Trig Database and the bwlch height derived from interpolation of 5m contouring.

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

The name of the hill is The Mount, and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it has minor roads to its north-west and north-east and the M4 motorway to its south, and is positioned between the city of Caerdydd (Cardiff) to the south-west and Casnewydd-ar-Wysg (Newport) to the north-east.

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 124m summit height, based on the spot height positioned at ST 25276 84738 that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating that the Ordnance Survey 1:50,000 Landranger map dated 1986 has a 127m spot height adjoined to a triangulation pillar and which is positioned at ST 25869 84831. As heights on 1:25,000 scale mapping were prioritised in this list over those on 1:50,000 scale mapping this hill’s summit was listed to where the 124m spot height appears on the 1:25,000 Explorer map.

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

Since publication of these P30 lists on Geoff Crowder’s v-g.me website the heights on different scaled Ordnance Survey maps can be cross referenced against a number of sources that are now available online, and 1:25,000 map data is no longer prioritised for summit heights over that of 1:50,000 map data, each is now assessed individually. Therefore, the 127m height given to the triangulation pillar is now prioritised for the summit height of this hill, this is not a substantial revision compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 127m and this was derived from the 127.247m flush bracket height adjoined to a triangulation pillar that once stood on the summit of this hill and which was destroyed in September 1985, this is 3m higher than the previously listed summit height of 124m which was derived from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Cymoedd Gwent

Name: The Mount

OS 1:50,000 map: 171

Summit Height (New height): 127m

Summit Grid Reference: ST 25868 84839

Bwlch Height: c 66m

Bwlch Grid Reference: ST 24800 87551

Drop: c 61m

Dominance: 48.03%

Myrddyn Phillips (August 2019)

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

Mynydd y Lan (ST 209 923) - 22nd significant height revision

Summit Relocations post for Mynydd y Lan

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

LIDAR image of Mynydd y Lan (ST 209 923)

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

Y Trichant – Welsh hills at or above 300m and below 400m in height with 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.

The name of the hill is Mynydd y Lan and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is encircled by roads with the B4251 to its south and west, the A472 to its north and the A467 and B4591 and the Afon Ebwy (Ebbw River) to its east, and has the town of Trecelyn (Newbridge) towards the north and the village of Pontycymer (Crosskeys) towards the east.

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 381m summit height, based on the spot height positioned at ST 20794 92508 that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating that the Ordnance Survey 1:50,000 Landranger map has a 385m spot height positioned at ST 20898 92357. As heights on 1:25,000 scale mapping were prioritised in this list over those on 1:50,000 scale mapping this hill’s summit was listed to where the 381m spot height appears on the 1:25,000 Explorer map.

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

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

When the Welsh Dominant list was originally compiled this hill was listed with 56.43% dominance based on its 381m summit spot height and its 166m bwlch spot height, with the latter appearing on the Ordnance Survey 1:25,000 Explorer map, with these values giving this hill 215m of drop.

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

LIDAR summit image of Mynydd y Lan

LIDAR bwlch image of Mynydd y Lan

The summit height produced by LIDAR analysis and its position in relation to the 385m spot 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. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

The summit height produced by LIDAR analysis is 381.3m and is positioned at ST 20903 92337, this is 3.7m lower than the 385m spot height that appears on the Ordnance Survey 1:50,000 Landranger map at approximately the same position.

The full details for the hill are:

Group: Cymoedd Gwent

Name: Mynydd y Lan

OS 1:50,000 map: 171

Summit Height (New height): 381.3m (LIDAR)

Summit Grid Reference: ST 20903 92337 (LIDAR)

Bwlch Height: 159.5m (LIDAR)

Bwlch Grid Reference: ST 19806 96725 (LIDAR)

Drop: 221.8m (LIDAR)

Dominance: 58.17% (LIDAR)

Myrddyn Phillips (July 2019)

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

Mynydd Bach (SH 389 767) - 21st significant height revision

Survey post for Mynydd Bach

Significant Name Changes post for Mynydd Bach

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 confirmed by LIDAR analysis, and a subsequent survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter taking place on the 28^th October 2018.

LIDAR summit image of Mynydd Bach

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

The name of the hill is Mynydd Bach and this was derived from local enquiry and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it has the A5 and A55 roads and the village of Gwalchmai towards its 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 listed with a summit height of c 95m, when this list was standardised with interpolated heights and drop values also included the hill was listed with an estimated c 97m summit height based on its uppermost 95m ring contour that appears 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 next re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online. This map has a 99m spot height in the vicinity of this hill’s summit, however this spot height is placed on a covered reservoir, and as this is considered a recent man-made construct it is not taken as a part of the hill’s overall height.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

The summit height produced by LIDAR is in good accordance with that produced by the Trimble GeoXH 6000 survey, and even though the spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website is placed on the top of a covered reservoir, this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 96.5m and this was derived from the Trimble GeoXH 6000 survey, this is 2.5m lower than the 99m spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map.

The full details for the hill are:

Group: Ynys Môn

Name: Mynydd Bach

OS 1:50,000 map: 114

Summit Height (New height): 96.5m (converted to OSGM15)

Summit Grid Reference: SH 38964 76773

Bwlch Height: c 64m

Bwlch Grid Reference: SH 40259 77918 (I)

Drop: c 32m

Dominance: 33.66%

For details on the summit survey of this hill

Myrddyn Phillips (May 2019)

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

Coed Darcy (SS 711 955) - 20th significant height revision

Hill Reclassifications post for Coed Darcy

Significant Name Changes post for Coed Darcy

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

LIDAR image of Coed Darcy (SS 711 955)

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 30m of 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 name the hill is now listed by is Coed Darcy and it is adjoined to the Fforest Fawr group of hills, which are situated in the northern part of South Wales (Region C, Sub-Region C2), and it is positioned with the B4290 and M4 roads to its east, and has the town of Castell-neth (Neath) 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 appeared in the accompanying Hills to be surveyed sub list as it did not meet the criteria then used for the main P30 list; however this sub list has now been standardised with drop values and interpolated heights also included in the main P30 and the accompanying sub list.

After this list was standardised and interpolated heights also included this hill was listed with 31m of drop and 37.35% of dominance, based on the 83m summit spot height that appears on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map and a bwlch height of 52m based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website

The summit height produced by LIDAR analysis is 80.4m and is positioned at SS 71147 95565, and the bwlch height is 53.0m and is positioned at SS 71330 95324, with these values giving this hill 27.4m of drop and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new summit height is 80.4m and this was produced from LIDAR analysis, this is 2.6m lower than its previously listed height of 83m which appears as a spot height on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map.

The full details for the hill are:

Group: Fforest Fawr

Name: Coed Darcy

OS 1:50,000 map: 170

Summit Height (New height): 80.4m (LIDAR)

Summit Grid Reference: SS 71147 95565 (LIDAR)

Bwlch Height: 53.0m (LIDAR)

Bwlch Grid Reference: SS 71330 95324 (LIDAR)

Drop: 27.4m (LIDAR)

Dominance: N/A, insufficient drop (LIDAR)

Myrddyn Phillips (May 2019)

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

Allt Wen (SH 745 772) - 19th significant height revision

Survey post for Allt Wen

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

Allt Wen (SH 745 772)

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

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

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

When the original Welsh 100m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 255m summit height based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

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

LIDAR image of Allt Wen

The summit height produced by the Trimble GeoXH 6000 survey is 252.3m, this is not a substantial revision when compared to some revised heights, and it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

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

The full details for the hill are:

Group: Carneddau

Name: Allt Wen

OS 1:50,000 map: 115

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

Summit Grid Reference: SH 74546 77264

Bwlch Height: 160.2m (converted to OSGM15)

Bwlch Grid Reference: SH 74855 77154

Drop: 92.1m

Dominance: 36.51%

For details on the survey of Allt Wen

Myrddyn Phillips (April 2019)

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

Llys y Gwynt (SH 779 728) - 18th significant height revision

Survey post for Llys y Gwynt

Significant Name Changes post for Llys y Gwynt

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 and its location, and the drop of the hill confirmed by LIDAR analysis, and a subsequent summit survey with the Trimble GeoXH 6000, both conducted by Myrddyn Phillips with the latter taking place on the 10^th October 2018.

Llys y Gwynt (SH 779 728)

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

The name of the hill is Llys y Gwynt, and it is adjoined to the Carneddau group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and is positioned with the B5106 to its west, the B5279 to its south and the Afon Conwy (River Conwy) to its east, and has the town of Conwy to its north.

When interpolated heights and drop values were added to the original Welsh 100m P30 list that was published on Geoff Crowder’s v-g.me website, this hill was listed with an estimated c 116m summit height based on interpolation of its uppermost 110m contour ring 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

LIDAR image of Llys y Gwynt

The summit height produced by the Trimble GeoXH 6000 survey is 120.6m, this is a substantial revision when compared to some revised heights, and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new listed summit height is 120.6m and this was produced by surveying with the Trimble GeoXH 6000, this is 4.6m higher than its previously listed height of c 116m which was based on interpolation of its uppermost 110m ring contour that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, however this new height is in accordance with the 5m contouring on OS Maps.

Extract from OSMaps showing an uppermost 120m ring contour

The full details for the hill are:

Group: Carneddau

Name: Llys y Gwynt

OS 1:50,000 map: 115

Summit Height (New height): 120.6m (converted to OSGM15)

Summit Grid Reference: SH 77982 72884

Bwlch Height: 50.7m (LIDAR)

Bwlch Grid Reference: SH 76137 71943 (LIDAR)

Drop: 70.0m (Trimble summit and LIDAR bwlch)

Dominance: 58.00% (Trimble summit and LIDAR bwlch)

For details on the summit survey of this hill

Myrddyn Phillips (March 2019)

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

Broughton Burrows (SS 413 927) - 17th significant height revision

Summit Relocations post for Broughton Burrows

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 hill’s height, drop and dominance confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Broughton Burrows

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

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 addition Welsh P30 hills whose prominence is 33.33% or more and below 50% of their absolute height. The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name of the hill is Broughton Burrows, and it is adjoined to the Gŵyr group of hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and it is positioned at the western end of the Gŵyr, and has the small community of Llangynydd towards the south-east.

Although the summit of this hill is not a part of open access land, and as such permission to visit should be sought, there is general acceptance for people to visit, with the nearest public footpath encircling the summit of the hill which comprises a dune system.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 49m summit height which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

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

When interpolated height and also drop values were added to these lists, this hill was listed with c 32m of drop based on the 49m spot height and an interpolated bwlch height of c 17m based on what was thought to be bwlch contouring between 15m – 20m as indicated on the 1:25,000 Explorer map. However, as this hill is a part of a dune system this map did not show continuous contours on either the summit or bwlch area of this hill.

Prior to LIDAR analysis this hill was analysed using the 5m contouring on OS Maps, which is the recent replacement for OS Get-a-map. The bwlch height was confirmed as being between 15m – 20m and an interpolated height of c 18m the listed. However, this mapping showed a number of 60m continuous ring contours for the summit area of this hill and therefore LIDAR was examined, with the summit height produced being 61.9m and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Extract from OS Maps

Therefore, this hill’s new summit height is 61.9m and this was produced from LIDAR analysis, this is 12.9m higher than its previously listed height of 49m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map, however this new height is in accordance with the 5m contouring on OS Maps.

LIDAR summit image of Broughton Burrows

Close up LIDAR summit image of Broughton Burrows

The full details for the hill are:

Group: Gŵyr

Name: Broughton Burrows

OS 1:50,000 map: 159

Summit Height (New height): 61.9m (LIDAR)

Summit Grid Reference: SS 41391 92781 (LIDAR)

Bwlch Height: 17.4m (LIDAR)

Bwlch Grid Reference: SS 41739 92663 (LIDAR)

Drop: 44.5m (LIDAR)

Dominance: 71.95% (LIDAR)

Myrddyn Phillips (December 2018)

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

Burry Holms (SS 398 926) - 16th 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 hill’s height, drop, dominance and status confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR summit image of Burry Holms

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

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 addition Welsh P30 hills whose prominence is 33.33% or more and below 50% of their absolute height. The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name of the hill is Burry Holms, and as this name implies the hill is a part of an island, and it is adjoined to the Gŵyr group of hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and is positioned at the western end of the Gŵyr, with the small community of Llangynydd towards the east south-east.

Although the island is not a part of open access land, and as such permission to visit should be sought, there is general acceptance for people to visit, with the nearest public footpath leading to the beach and island to the east on the western part of Broughton Burrows.

When the original Welsh 30-99m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 35m summit height based on information from David Purchase who had noted a 35m spot height on the Ordnance Survey 1:10,000 map.

Prior to LIDAR analysis the uppermost 30m ring contour on contemporary Ordnance Survey maps had been interpolated, giving an estimated summit height of c 33m. However, even though the 1:10,000 mapping is prioritised over this interpolated summit height, the 35.1m height produced by LIDAR analysis still comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, this hill’s new summit height is 35.1m and this was produced from LIDAR analysis, this height is only 0.1m higher than the previously listed height of 35m which was derived from the Ordnance Survey 1:10,000 map, but it is 2.1m higher than the interpolated height of c 33m taken from contemporary Ordnance Survey maps.

LIDAR bwlch image of Burry Holms

The full details for the hill are:

Group: Gŵyr

Name: Burry Holms

OS 1:50,000 map: 159

Summit Height (New height): 35.1m (LIDAR)

Summit Grid Reference: SS 39863 92603 (LIDAR)

Bwlch Height: 0.3m (LIDAR)

Bwlch Grid Reference: SS 40173 92525 (LIDAR)

Drop: 34.8m (LIDAR)

Dominance: 99.02% (LIDAR)

Myrddyn Phillips (December 2018)

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

Ynys Deullyn (SM 844 340) - 15th significant height revision

Hill Reclassifications post for Ynys Deullyn

There has been a Significant Height Revision to a hill that appears in the following lists; 30-99m Twmpau and Y Trechol – The Dominant Hills of Wales, with the hill’s height, drop, dominance and status confirmed by LIDAR analysis conducted by Myrddyn Phillips.

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have a minimum 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.

The name of the hill is Ynys Deullyn and as its name implies it is an island, or more strictly speaking a tidal island that is attached to mainland Wales at low tide. The hill is adjoined to the Carn Llidi group of hills, which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4), with the island being positioned on the northern part of the Pembrokeshire coast, and it has the small community of Abercastell towards its west south-west.

If wanting to visit the island permission to do so should be sought as it is not a part of designated open access land, for those wishing to do so caution is advised as the easiest approach will probably necessitate some form of scramble.

This hill did not appear in the main P30 list or the accompanying Hills to be surveyed sub list when the original Welsh P30 hills were published on Geoff Crowder’s v-g.me website, as it was thought not to have 30m of drop and did not meet the criteria then used for the sub category; however this sub list has now been standardised including the addition of interpolated drop and height values.

This hill was included as a P30 shortly after the Ordnance Survey Interactive Coverage Map became available on the Geograph website, and prior to LIDAR analysis it was listed with 30m of drop based on the 30m summit spot height that appears on this map.

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

The summit height produced by 2m DSM LIDAR analysis is 32.6m, this is not a dramatic height revision when compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

2m DSM LIDAR image of Ynys Deullyn (SM 844 340)

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 by LIDAR analysis, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new summit height is 32.6m and this was produced from LIDAR analysis, this is 2.6m higher than its previously listed height of 30m which appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

The full details for the hill are:

Group: Carn Llidi

Summit Height (New Height): 32.6m (LIDAR)

Name: Ynys Deullyn

OS 1:50,000 map: 157

Summit Grid Reference: SM 84479 34095 (LIDAR)

Drop: 30.5m (LIDAR)

Dominance: 93.51% (LIDAR)

Myrddyn Phillips (September 2018)

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

Fegla Fach (SH 638 153) - 14th significant height revision

Survey post for Fegla Fach

Hill Reclassifications post for Fegla Fach

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, drop, dominance and status of the hill confirmed by a combination of LIDAR analysis and a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

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

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.

The name of the hill is Fegla Fach 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), with the hill being positioned between the Afon Mawddach to its north-west and the A 493 road to its south-east, and has the village of Y Friog (Fairbourne) to the south-west.

As the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so access to its summit can be found from the confines of a camp site which is situated at the base of the hill to its south-west.

Prior to LIDAR analysis and the Trimble survey this hill was listed with 25m of drop based on the 28m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 3m bwlch spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

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

The summit height produced by LIDAR analysis is 31.5m, this is not a dramatic height revision when compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

LIDAR image of Fegla Fach (top right of photograph) and showing the Arthog bog

Therefore, this hill’s new summit height is 31.5 and this was produced by LIDAR analysis, this is 3.5m higher than its previously listed height of 28m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Cadair Idris

Summit Height (New Height): 31.5m (LIDAR)

Name: Fegla Fach

OS 1:50,000 map: 124

Summit Grid Reference: SH 63818 15311 (LIDAR)

Drop: 30.0m (LIDAR summit and Trimble bwlch)

Dominance: 95.37% (LIDAR summit and Trimble bwlch)

The summit of Fegla Fach (SH 638 153)

For details on the survey and on-site visit that significantly revised the summit height of this hill

Myrddyn Phillips (August 2018)

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

Fegla Fawr (SH 629 146) - 13th significant height revision

Survey post for Fegla 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, drop and dominance of the hill confirmed by a Trimble GeoXH 6000 survey and LIDAR analysis conducted by Myrddyn Phillips.

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

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.

The name of the hill is Fegla Fawr 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), with the hill being positioned between the Afon Mawddach to its north-west and north and the A 493 road to its south-east, and has the village of Y Friog (Fairbourne) to the south-west.

As the hill is not a part of designated open access land permission to visit should be sought, however there are paths leading toward its summit which is an indicator that local concession exists to visit it summit.

Prior to LIDAR analysis and the Trimble survey this hill was listed with c 55m of drop based on an estimated c 57m summit height with the hill having an uppermost 50m ring contour on contemporary Ordnance Survey maps, and a bwlch height of 2m based on the spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.

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

LIDAR image of Fegla Fawr

The summit height produced by the Trimble GeoXH 6000 survey is 59.5m (converted to OSGM15), this is not a dramatic height revision when compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, this hill’s new summit height is 59.5m (converted to OSGM15) and this was produced by the Trimble GeoXH 6000 survey, this is 2.5m higher than its previously listed height of c 57m which was estimated from the uppermost 50m ring contour on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group: Cadair Idris

Summit Height (New Height): 59.5m (converted to OSGM15)

Name: Fegla Fawr

OS 1:50,000 map: 124

Summit Grid Reference: SH 62966 14665

Drop: 57.6m (Trimble summit and LIDAR bwlch)

Dominance: 96.81% (Trimble summit and LIDAR bwlch)

Gathering data at the summit of Fegla Fawr (SH 629 146) which resulted in this hill's significant height revision

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

Myrddyn Phillips (August 2018)

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

Upper Park (SJ 189 052) - 12th significant height revision

Survey post for Upper Park

Summit Relocation post for Upper Park

There has been a Significant Height Revision to a hill that is listed in the Y Trichant and Y Trechol – The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that confirmed this height revision being conducted on the 7^th January 2018.

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

Y Trichant - Welsh hills at and above 300m and below 400m in height that have 30m minimum drop.

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height. With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The name of the hill is Upper Park and it is situated in the Carnedd Wen range of hills which are in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned between the A 458 road to its north and the A 483 road to its south-east, and has the town of Y Trallwng (Welshpool) to its north-east.

As the summit of the hill is not on designated open access land and is part of a private estate permission to visit should be sought, for those wishing to do so there are a number of options for an ascent, all of which use tracks through forested plantations.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was originally listed as 352m, with this taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, latterly the hill has been listed with an estimated c 353m summit height.

The 354.0m (converted to OSGM15) summit height produced by the Trimble GeoXH 6000 is not a dramatic increase from the 352m spot height, but does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose 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, and also hill’s that do not possess a summit spot height and whose estimated summit height has a 2m or more discrepancy when compared to data produced either by the Trimble or by LIDAR. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new summit height is 354.0m (converted to OSGM15) which is 2.0m higher than the 352m spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Carnedd Wen

Summit Height (New Height): 354.0m (converted to OSGM15)

Name: Upper Park

OS 1:50,000 map: 125

Summit Grid Reference: SJ 18980 05270

Drop: 177.0m (converted to OSGM15)

Dominance: 49.998%

The Trimble GeoXH 6000 gathering data at the summit of Upper Park (SJ 189 052) which resulted in this hill's significant height revision

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

Myrddyn Phillips (February 2018)

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

Bryn y Gwynt (SH 599 449) - 11th significant height revision

Hill Reclassifications post for Bryn y Gwynt

Significant Name Changes post for Bryn y Gwynt

Summit Relocations post for Bryn y Gwynt

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

LIDAR image of Bryn y Gwynt (SH 599 449)

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

The name the hill is listed by is Bryn y Gwynt and this was derived from local enquiry and the series of Ordnance Survey Six-Inch maps and it is situated in the Moelwynion range of hills in the Region of North Wales (Region A, Sub-Region A1), and is positioned with the A 4085 road to its north-east and has the Welsh Highland Railway to its immediate west and overlooks the Afon Glaslyn also to its west, and has the village of Beddgelert to its north north-west and the town of Porthmadog to its south south-west.

The hill is a part of Coed Hafod y Llyn, and as this name implies its summit is placed in woodland which is deciduous, and as the summit is not a part of designated open access land permission to visit should be sought, however paths are indicated on the map to the north, east and south of this hill’s summit and therefore gaining access to its lower slopes has probably been accepted for many years.

Prior to LIDAR analysis this hill was listed in the Hills to be surveyed sub list that accompanied the Welsh P30 lists published on Geoff Crowder’s v-g.me website. When these sub lists were standardised and also drop values added, this hill was listed with an estimated c 29m of drop based on the 56m spot height that appears on the Ordnance Survey 1:25,000 Explorer map at SH 59881 44828 and an estimated bwlch height of c 27m based on contouring at 10m intervals between 20m – 30m, with the caveat that the 27m spot height that appears on a road at SH 60168 45293 on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website is judged not to be positioned at the critical bwlch.

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

The summit height produced by LIDAR analysis is 58.4m and is positioned at SH 59949 44915, but as the summit has now been surveyed with the Trimble GeoXH 6000 giving 59.9m positioned at SH 59949 44919, it is this result that is being prioritised for listing purposes. This is not a dramatic height revision when compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose 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. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

The Trimble GeoXH 6000 gathering data at the summit of Bryn y Gwynt

Therefore, the new listed summit height of this hill is 59.9m and this was derived from a Trimble GeoXH 6000 survey, this is 3.9m higher than its previously listed height of 56m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Moelwynion

Name: Bryn y Gwynt

OS 1:50,000 map: 124

Summit Height (New Height): 59.9m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference: SH 59949 44919 (Trimble GeoXH 6000)

Bwlch Height: 28.0m (LIDAR)

Bwlch Grid Reference: SH 60224 45248 & SH 60226 45258 & SH 60227 45259 (LIDAR)

Drop: 31.9m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance: 53.21% (Trimble GeoXH 6000 summit and LIDAR bwlch)

My thanks to Aled Williams for sending the details of this hill to me.

Myrddyn Phillips (February 2018)

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

Bryn Tŵr (SH 604 441) - 10th significant height revision

Survey post for Bryn Tŵr

Summit Relocation post for Bryn Tŵr

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, and which was initiated by a survey with the Trimble GeoXH 6000 which took place on the 23^rd December 2017 in wet conditions but with clear visibility.

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

30-99m Twmpau – Welsh hills at and above 30m and below 100m in height that have 30m minimum drop. With the word Twmpau being an acronym standing for ‘thirty welsh metre prominences and upward’.

Y Trechol – The Dominant Hills of Wales - Welsh P30s whose prominence equal or exceed half that of their absolute height.

The name of the hill is Bryn Tŵr and it is placed in the Moelwynion range of hills which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and the hill is positioned overlooking the A 4085 road and the Nanmor to its east, with it being positioned between the village of Beddgelert to its north north-west and Porthmadog to its south south-west.

As the summit of the hill is not on designated open access land permission to visit should be sought, however the hill has a well-used path leading to its summit indicating that people have visited this hill for many years.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with c 40m of drop and 76.92% Dominance based on the 52m spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website and an estimated bwlch height of c 12m based on contouring between 10m – 20m. The summit height produced by the Trimble survey is 54.5m (converted to OSGM15) with its position to the west of where the 52m spot height appears and outside of the uppermost 50m ring contour on Ordnance Survey maps, with this summit height coming 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 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 a previous estimated summit height based on interpolation of contours. Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new summit height is 54.5m (converted to OSGM15) which is 2.5m higher than its previously listed height of 52m and 14.5m higher than the uppermost 40m ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Group: Moelwynion

Summit Height (New Height): 54.5m (converted to OSGM15)

Name: Bryn Tŵr

OS 1:50,000 map: 124

Summit Grid Reference: SH 60453 44187

Drop: c 43m

Dominance: 77.99%

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

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

Myrddyn Phillips (January 2018)

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

Gallt y Gog (SH 751 012) - 9th significant height revision

Survey post for Gallt y Gog

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, due to a survey with the Trimble GeoXH 6000 which took place on the 29^th October 2017 and conducted by Myrdyn Phillips.

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

30-99m Twmpau – Welsh hills at and above 30m and below 100m in height that have 30m minimum drop. With the word Twmpau being an acronym standing for ‘thirty welsh metre prominences and upward’.

Y Trechol – The Dominant Hills of Wales - Welsh P30s whose prominence equal or exceed half that of their absolute height.

The name of the hill is Gallt y Gog and it is placed in the Pumlumon range of hills which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and the hill is positioned overlooking the A 489 road to its south and the Afon Dyfi to its north, with the town of Machynlleth at the base of the hill to the south.

As the summit of the hill is not on designated open access land permission to visit should be sought, for those wishing to do so the nearest open access land is to the south-west of the hill, however there are paths in the conifer plantation that covers this hill’s summit and these indicate that people have visited this hill for many years.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with c 66m of drop and 72.53% dominance based on an estimated summit height of c 91m which was based on a 90m uppermost contour, and an estimated bwlch height of c 25m, with the summit height produced by the Trimble being 87.5m (converted to OSGM15), with this summit height coming 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 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 a previous estimated summit height based on interpolation of contours. Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

However, although the 5-15cm: 43.58% Estimated Accuracy recorded by the Trimble GeoXH 6000 is reasonable considering that the survey took place within a wood; the Standard Deviation of 0.5m signifies that the accuracy of the data set is questionable. To compound this uncertainty there is question whether the uppermost 90m contour on Ordnance Survey maps is erroneous as it is placed a significant distance from where the accepted summit position of this hill is situated, according to the map the accepted summit position on the ground is above 80m but below the 90m contour. However, this 90m uppermost contour could in fact be a depression and this ring contour signifies a 70m height, with the uppermost contour on Ordnance Survey maps being 80m, whatever the uncertainty, the result produced by the Trimble GeoXH 6000 for the summit of this hill does come within the above specified parameters.

Therefore, this hill’s new summit height is 87.5m (converted to OSGM15) which is 3.5m lower than its previously estimated height of c 91m and 2.5m lower that what is thought to be the uppermost ring contour on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group: Pumlumon

Name: Gallt y Gog

OS 1:50,000 map: 135

Summit Height (New Height): 87.5m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference: SH 75169 01223 (Trimble GeoXH 6000)

Bwlch Height: 24.7m (LIDAR)

Bwlch Grid Reference: SH 75589 00921 (LIDAR)

Drop: 62.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance: 71.74% (Trimble GeoXH 6000 summit and LIDAR bwlch)

The Trimble GeoXH 6000 gathering data at the summit of Gallt y Gog (SH 751 012) which resulted in this hill's significant height revision

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

Myrddyn Phillips (January 2018)

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

Mynydd Epynt (SN 961 464) - 8th significant height revision

Survey post for Mynydd Epynt

1st Significant Name Changes post

2nd Significant Name Changes post

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau and Y Trechol - The Dominant Hills of Wales, and which was initiated by analysis of LIDAR data by Aled Williams and a subsequent survey with the Trimble GeoXH 6000, with the survey that confirmed this height revision being conducted on the 28th December 2016.

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

Y Pedwarau - Welsh hills at and above 400m and below 500m in height that have 30m minimum drop.

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height. With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The name of the hill is Mynydd Epynt and it is situated in the hills of Mynydd Epynt in the south-easterly part of Mid and West Wales (Region B, Sub-Region B2), and the survey was conducted on a beautiful winter’s morning with blue sky, frost and just a breath of breeze. Large swathes of Mynydd Epynt is out of bounds for much of the year as it forms part of the Sennybridge Artillery Range Firing Area, and the hill range is positioned between those of Mynydd Du, Fforest Fawr, Bannau Brycheiniog (Brecon Beacons) and Mynyddoedd Duon (Black Mountains) to its south and the wilds of the Elenydd to its north.

The hill is situated just above the high point of the B 4519 as it climbs from the small community of Garth to the north toward the village of Upper Chapel to the south-east, the hill should only be ascended when it is appropriate to do so due to the presence of the military, otherwise it would be an easy ascent on a track from a car parking area near to the top of the road to the north-east of the summit.

The survey with the Trimble GeoXH 6000 was preceded with analysis of LIDAR data. LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales.

Aled’s analysis of LIDAR data gives the hill the following details:

Mynydd Epynt

Summit Height: 475.5m

Summit Grid Reference: SN 96120 46434

Prior to the analysis of LIDAR data and surveying the hill with the Trimble GeoXH 6000, Mynydd Epynt was listed with a 478m summit height based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, this height seems to be a relatively recent addition as no spot height is shown on any Ordnance Survey map examined prior to and including the historical 1:25,000 map.

Mynydd Epynt was surveyed with the Trimble GeoXH 6000 giving the hill the following details:

Summit Height: 475.7m (475.681m converted to OSGM15)

Summit Grid Reference: SN 96124 46428

This is not a dramatic height revision when compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.

The summit of the hill consists of red grass that when last visited had been fenced with stakes and a single wire that is easy to either clamber under or as I found; over. The ground hereabouts is mainly hidden by the length of the reed grass but the high point is accepted as being beside a small concrete pillar and this is where the Trimble GeoXH 6000 was set up. Therefore this hill’s new summit height as surveyed by the Trimble GeoXH 6000 is 475.7m (converted to OSGM15) which is 2.3m lower than its previously listed height of 478m which appears on the Ordnance Survey enlarged mapping hosted on the Geograph website and the 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Group: Mynydd Epynt

Summit Height (New Height): 475.7m (converted to OSGM15)

Name: Mynydd Epynt

OS 1:50,000 map: 147

Summit Grid Reference: SN 96124 46428

Drop: c 198

Dominance: 41.62%

The Trimble GeoXH 6000 gathering data at the summit of Mynydd Epynt (SN 961 464) which confirmed this hill's significant height revision

For details on the survey that confirmed the significant height revision of this hill

Myrddyn Phillips and Aled Williams (January 2017)

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

Mynydd yr Hewyrch (SH 816 150) - 7th significant height revision

Summit survey post for Mynydd yr Hewyrch

Bwlch survey post for Mynydd yr Hewyrch

There has been a Significant Height Revision to a hill that is listed in the Yr Uchafion, 600m Twmpau and Y Trechol - The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000 and a survey with the Leica RX1250, with the survey that resulted in this height revision being conducted on the 2oth October 2016 in good, clear and calm conditions in the company of Alan Dawson.

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

Yr Uchafion - All Welsh hills at or above 500m in height that have 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams.

600 Twmpau - These are the Welsh hills at or above 600m and below 700m in height that have a minimum drop of 30m. The word Twmpau is an acronym for thirty welsh metre prominences and upward, and the list is authored by Myrddyn Phillips.

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height. The list is authored by Myrddyn Phillips.

The name that the hill is currently listed by is Mynydd yr Hewyrch and it is situated in the hills of the Rhwng Dyfi a Dulas range which have been referred to as the Bryniau Dyfi and which are situated in the south-western part of north Wales, with the survey of this hill conducted during the late afternoon in the company of Alan Dawson, who had suggested the walk and also surveyed the hill with his Leica RX1250, and it is the result from the Leica equipment that is being used for this hill's data.

The hill is situated between the Afon Cerist and the A 470 road to its north and the conifer plantation of the Dyfi Fforest (Dovey Forest) to its south and is positioned above the small community of Dinas Mawddwy to its east, and the hill can be easily accessed from a lane leading to a path that heads for the summit via the escarpment edge above Craig Maesglase, or via the north-eastern ridge that heads straight for the summit of its adjacent top; Maen Du.

Prior to the survey with the Leica RX1250 and the Trimble GeoXH 6000 the height of the hill was listed as 676m based on the summit spot height on the Harvey 1:40,000 Britain Mountain Map. However, the summit of Mynydd yr Hewyrch only has a 670m uppermost contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps with the adjacent summit of Maen Du at SH 822 151 being given a 674m spot height, because of this the summit of Maen Du was previously listed as that for the hill, and the higher summit of Mynydd yr Hewyrch is therefore a recent addition and first noted by Tim Jones who reported that he believed this summit to be higher to John and Anne Nuttall in 1996.

Three points were surveyed for summit position using the Trimble GeoXH 6000 and the Leica RX1250, each position being close in height and taken to ground consisting of moorland peat hags rising above a shapely large pool which is positioned on the summit area.

The 678.5m (converted to OSGM15) height produced by the Leica RX1250 is 2.5m higher than the previously listed height of 676m, which was based on the Harvey British Mountain Map spot height, and 8.5m higher than the uppermost contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and therefore comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose 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, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised in favour of the 1:50,000 for detailing these revisions.

The summit of this hill consists of ground at the top of a moorland peat hag, and therefore this hill’s new summit height as surveyed by Alan Dawson with the Leica RX1250 is 678.5m (converted to OSGM15) which is 2.5m higher than its previously listed height of 676m which appears on the Harvey 1:40,000 British Mountain Map and 8.5m higher than the uppermost 670m contour ring on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill: Mynydd yr Hewyrch

Summit Height (New Height): 678.5m (converted to OSGM15, Leica RX1250)

Name: Mynydd yr Hewyrch

OS 1:50,000 map: 124, 125

Summit Grid Reference: SH 81697 15003

Drop: 318.0m (converted to OSGM15, Trimble GeoXH 6000 bwlch)

Dominance: 46.87%

The Trimble GeoXH 6000 gathering data at one of the three positions surveyed atop Mynydd yr Hewyrch which when coupled with the Leica RX1250 survey resulted in this hill's significant height revision

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

Myrddyn Phillips and Aled Williams (November 2016)

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

Emsger (SM 651 226) - 6th significant height revision

Survey post for Emsger

There has been a Significant Height Revision to a hill that is listed in the Y Pellennig, 30-99m Twmpau and Y Trechol - The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that resulted in this height revision being conducted on the 14^th May 2016 in good, bright conditions, perched beside a lighthouse on one of the most remote places in the whole of Wales.

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

Y Pellennig –The Remotest Hills of Wales comprise all Welsh hills whose summit is 2.5km or more from the nearest paved public road and which have a minimum 15m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams.

30-99m Twmpau - These are the Welsh hills at or above 30m and below 100m in height that have a minimum drop of 30m. The word Twmpau is an acronym for thirty welsh metre prominences and upward, and the list is authored by Myrddyn Phillips.

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height. The list is authored by Myrddyn Phillips.

The hill is positioned on the island known as Emsger, which is also commonly known as South Bishop. This island is positioned an approximate 8km (5 miles) west of St David’s Head in western Pembrokeshire, and unless being a competent and enthusiastic seal, it can only be approached by boat. The island forms a part of the Bishops and Clerks chain of islands which form a compact groups of islets; all are rocky and are aligned northward to southward with North Bishop, Carreg Rhoson, Daufraich and Emsger being the main named island in each small group.

The island is predominantly rock and if not for a series of steps leading up toward its summit its ascent would no doubt prove more problematic. The upper part of Emsger has a lighthouse on it; this was built in 1839, and was converted to operating by electric in 1959, and demanned and automated in 1983.

The upper part of the island now has the lighthouse and associated buildings and platforms built on it, and therefore what once constituted the natural summit of the island is either buried under the lighthouse / platforms or it was destroyed during construction of the lighthouse.

I visited Emsger with Adrian Rayner, Ayako, Rob Woodall, Jon Glew, Sheila Glew, Sarah Kerr and Bob Kerr, and a quick assessment of what is left of natural ground pinpointed that this is situated just to the south-west of the main southerly corner of the lighthouse and its grounds. This position was adjacent to steps leading down to the island’s helipad.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with a 37m summit height, which originates from the spot height on the Ordnance Survey 1:25,000 Explorer map, with the spot of this spot height positioned on the south-east part of the land immediately adjacent to the lighthouse. This is on a part of the construction and is man-made; however natural ground exists close to this point but it is significantly lower.

Therefore this island’s new summit height is 33.8m (converted to OSGM15) which is 3.2m lower than its previously listed height of 37m which appears on Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Island: Bishops and Clerks

Summit Height: 33.8m (converted to OSGM15)

Name: Emsger

OS 1:50,000 map: 157

Summit Grid Reference: SM 65116 22619

Drop: 33.8m (converted to OSGM15)

Dominance: 100.00%

The Trimble GeoXH 6000 gathering data 0.99m above the highest remaining natural ground at the summit of Emsger, otherwise known as South Bishop (SM 651 226) which resulted in this island's significant height revision

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

Myrddyn Phillips (June 2016)

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

Bryn Maelgwyn (SH 795 805) - 5th significant height revision

Survey post for Bryn Maelgwyn

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 a Trimble GeoXH 6000 summit survey and LIDAR bwlch analysis conducted by Myrddyn Phillips.

LIDAR image of Bryn Maelgwyn (SH 795 805)

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 by Myrddyn Phillips

The name the hill is now listed by is Bryn Maelgwyn and it is adjoined to the Mynydd Hiraethog group of hills, which are situated in the northern part of North Wales (Region A, Sub-Region A2), and it is positioned with the B5115 road to its north, the A470 road to its west and minor roads to its south-east and north-east, and has the town of Llandudno towards the north-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 non-interpolated summit height of c 100m, based on the uppermost contour that appears on the Ordnance Survey 1:25,000 Explorer map.

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with an estimated c 43m of drop, based on an estimated c 106m summit height and an estimated c 63m bwlch height, with both heights based on interpolation of 5m contouring that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

The summit height produced by the Trimble GeoXH 6000 survey is 102.1m positioned at SH 79580 80540, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The Trimble GeoXH 6000 gathering data from the summit of Bryn Maelgwyn

Therefore, the new listed summit height of this hill is 102.1m and this was derived from a Trimble GeoXH 6000 survey, this is 3.9m lower than the previously listed summit height of c 106m, which was based on interpolation of 5m contouring on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

The full details for the hill are:

Group: Mynydd Hiraethog

Name: Bryn Maelgwyn

OS 1:50,000 map: 115

Summit Height (New Height): 102.1m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference: SH 79580 80540 (Trimble GeoXH 6000)

Bwlch Height: 63.5m (LIDAR)

Bwlch Grid Reference: SH 79893 80558 (LIDAR)

Drop: 38.5m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance: 37.76% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips (January 2016)

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

Bryn Mawr (SJ 251 190) - 4th significant height revision

Survey post for Bryn Mawr

Hill Reclassifications post for Bryn Mawr

There has been a Significant Height Revision to a hill listed in the 100m Twmpau and Y Trechol - The Dominant Hills of Wales, and which was initiated by a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted on 8^th August 2015.

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

100m Twmpau - These are the Welsh hills at or above 100m and below 200m in height that have a minimum drop of 30m. The word Twmpau is an acronym for thirty welsh metre prominences and upward.

Y Trechol - The Dominant Hills of Wales - These are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height.

The name of the hill is Bryn Mawr and it is situated in the lower hills of the Carnedd Wen range, and is positioned above the small community of Four Crosses which is situated beside the Afon Efyrnwy (River Vyrnwy) and part of the Montgomeryshire Canal.

The hill was surveyed in the company of Alex Cameron during a multi hill bagging day when the weather was set fine and we visited nine P30 Twmpau hills with seven of them being Trimbled.

Access to Bryn Mawr is good from the west of its summit, as there is sufficient parking close to a gate that accesses a field to another gate which leads on to the hill. However, the upper section is overgrown and the ancient earthen embankments of its hill fort are now immersed in long grass, nettles and brambles. The summit is easily identified and the hill is recommended as there is a peaceful ambiance to it.

The hill has a 170m uppermost contour ring on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, with the latter having contour intervals at 5m. Prior to the survey with the Trimble GeoXH 6000 the hill had been listed with an estimated summit height of c 174m based on the dimensions of the uppermost contour in relation to the steepness of the surrounding ground, with the height resulting from the survey with the Trimble GeoXH 6000 being 178.1m (converted to OSGM15).

Therefore this hill’s new summit height is 178.1m (converted to OSGM15) which is 4.1m higher than its previously estimated height of c 174m and 8.1m higher than its uppermost ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill: Carnedd Wen

Summit Height (New Height): 178.1m (converted to OSGM15)

Name: Bryn Mawr

OS 1:50,000 map: 126

Summit Grid Reference: SJ 25117 19054

Drop: 90m

Dominance: 50.53%

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

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

Myrddyn Phillips (September 2015)

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

Pen y Berth (SJ 081 127) - 3rd significant height revision

Summit survey post for Pen y Berth

Bwlch survey post for Pen y Berth

Summit Relocations post for Pen y Berth

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

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

200m Twmpau - these are the Welsh hills at or above 200m and below 300m in height that have a minimum drop of 30m.

Y Trechol - The Dominant Hills of Wales - these are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height. With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

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

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

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

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

Western 282m spot height at SJ 08012 12780 not surveyed

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

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

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

The full details for the hill are:

Cardinal Hill: Carreg y Big

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

Name: Pen y Berth

OS 1:50,000 map: 125

Summit Grid Reference: SJ 08126 12730

Drop: 134.2m (converted to OSGM15)

Dominance: 46.68%

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

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

Myrddyn Phillips (August 2015)

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

Coed y Gaer (SO 004 843) - 2nd significant height revision

Survey post for Coed y Gaer

Hill Reclassifications post for Coed y Gaer

Subsequent LIDAR analysis negates the need for this Significant Height Revision post. However, it is being kept with the results from LIDAR analysis prioritised in preference to those from the Trimle GeoXH 6000 survey.

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to the listing of Y Trichant - The 300m Hills of Wales and Y Trechol - The Dominant Hills of Wales, with the following details being retrospective as the survey that resulted in this height revision was conducted on 9^th February 2014. The hill is listed as a Lesser Dominant as well as a Trichant, with the latter being the 300m height band of Twmpau (thirty welsh metre prominences and upward) hills.

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

Y Trichant - The 300m Hills of Wales - these are the Welsh hills at or above 300m and below 400m in height that have a minimum drop of 30m.

Y Trechol - The Dominant Hills of Wales - these are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height. With the criteria for Lesser Dominant status being those addition Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

The name the hill is listed y is Coed y Gaer and it is situated in the Hirddywel range of hills to the east of Llanidloes, and the survey was conducted in the company of Mark Trengove on a particularly wet and cold day. The hill can be accessed from a minor lane to the south of its summit; and it overlooks the A470 and the Afon Hafren (River Severn) which are to its north-west.

The height given the hill on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map is 362m, with the height resulting from the survey with the Trimble being 359.9m (converted to OSGM15). This is not a dramatic height revision but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the surveyed height produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.

LIDAR image of Coed y Gaer (SO 004 843)

The full details for the hill are:

Cardinal Hill: Pegwn Mawr

Summit Height (New Height): 361.0m (LIDAR)

Name: Coed y Gaer

OS 1:50,000 map: 136

Summit Grid Reference: SO 00491 84393 (LIDAR)

Drop: 121.5m (LIDAR)

Dominance: 33.65% (LIDAR)

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

Myrddyn Phillips (August 2015)

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

Ynys Hir (SH 566 396) - 1st significant height revision

Survey post for Ynys Hir

Hill Reclassifications post for Ynys Hir - 30-99m Twmpau

Hill Reclassifications post for Ynys Hir - Y Trechol - The Dominant Hills of Wales

There has been a Significant Height Revision to the 30-99m Twmpau and Y Trechol - The Dominant Hills of Wales listings initiated by a survey with the Trimble GeoXH 6000, with the following details being retrospective as the survey that resulted in this height revision was conducted on 1^st February 2014.

The two listings that this height revision affects are:

30-99m Twmpau - these are the Welsh hills at or above 30m and below 100m in height that have a minimum drop of 30m.

Y Trechol - The Dominant Hills of Wales - these are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height.

The name of the hill is Ynys Hir and it is situated in the lowlands outside of Porthmadog in north-west Wales, and the survey was conducted in the company of Aled Williams who had suggested the walk as he considered at least one of the hills he proposed for us to visit would become a new P30 – he was right!

The hill is situated to the north of Porthmadog in the area known as Traeth Mawr, and it can be easily accessed from a lay-by on the A487 to the south-west. The term easily accessed is only applicable to where the road is situated in relation to the hill as it can be a bit of a battle to reach its top.

The summit height of Ynys Hir has been dramatically increased from its current Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map height, as prior to the survey with the Trimble GeoXH 6000 the hill was not listed as it only had an uppermost ring contour of 20m on both of these maps, with an estimated summit height of c 23m. Its new summit height is 37.3m (converted to OSGM15), which is 14.3m higher than its previously estimated height and 17.3m higher than the 20m uppermost ring contour on the current Ordnance Survey maps.

Although the new summit height of 37.3m (converted to OSGM15) is dramatically different to current Ordnance Survey map detail, the Ordnance Survey Historical 1:25,000 map has an uppermost ring contour of 100ft for this hill which is correct when compared to the surveyed height produced by the Trimble GeoXH 6000.

The full details for the hill are:

Cardinal Hill: Hir Ynys

Summit Height (New Height): 37.3m (converted to OSGM15)

Name: Ynys Hir

OS 1:50,000 map: 124

Summit Grid Reference: SH 56695 39693

Drop: c 34m

Dominance: 91.21%

Beyond the trees, vertical cliffs and undergrowth is the summit of Ynys Hir, a new P30 which has a significant height revision

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

Myrddyn Phillips (August 2015)

Monday 13 November 2017

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

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