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

Monday, 23 October 2017

Mapping Mountains – Significant Height Revisions – Y Pedwarau - The 400m Hills of Wales

Y Pedwarau - The 400m Hills of Wales – Significant Height Revisions

Y Pedwarau - The 400m Hills of Wales are the Welsh hills at or above 400m and below 500m in height that have a minimum drop of 30m. Accompanying the main P30 list are five sub lists; these are the 500m Sub-Pedwar, 500m Double Sub-Pedwar, 400m Sub-Pedwar, 390m Sub-Pedwar and 390m Double Sub-Pedwar category’s, with their criteria detailed in the respective Change Registers that have been created and which are linked in their above titles, with the Introduction to this list being published on Mapping Mountains on the 30^th January 2017.

The list is co-authored by Myrddyn Phillips and Aled Williams and the posts that have appeared on Mapping Mountains detailing the significant height revisions to the main P30 list and the sub lists appear below presented chronologically in receding order.

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Bryn Berw (SN 714 505) - 26th significant height revision

LIDAR image of Bryn Berw (SN 714 505)

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

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills, with this hill being included in the 400m Sub-Pedwar category. The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Bryn Berw, and it is adjoined to the Esgair Wen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north-east and west, and has the village of Llanddewibrefi towards the north-west.

When the original 400m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the accompanying Hills to be surveyed sub list with a non-interpolated 430m summit height.

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 28m of drop, based on the 433m summit spot height and the 405m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. And these are the details the hill was listed by when the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013.

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 Bryn Berw (SN 714 505)

LIDAR analysis gives the highest ground on this hill as 430.7m positioned at SN 71433 50501, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 430.7m and this was derived from LIDAR analysis, this is 2.3m lower than the previously listed summit height, which was based on the 433m spot height that appeared 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: Esgair Wen

Name: Bryn Berw

OS 1:50,000 map: 146, 147

Summit Height (New Height): 430.7m (LIDAR)

Summit Grid Reference: SN 71433 50501 (LIDAR)

Bwlch Height: 403.3m (LIDAR)

Bwlch Grid Reference: SN 71373 50607 (LIDAR)

Drop: 27.4m (LIDAR)

Myrddyn Phillips and Aled Williams (March 2026)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Wenallt (SN 967 784) - 25th significant height revision

Summit Relocations post for Wenallt

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips.

LIDAR image of Wenallt (SN 967 784)

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

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills; 500m Sub-Pedwarau, 500m Double Sub-Pedwarau, 400m Sub-Pedwarau, 390m Sub-Pedwarau and the 390m Double Sub-Pedwarau. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Wenallt, and it is adjoined to the Hirddywel group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B2), and it is positioned with a minor road to its north-west and south, the A470 road to its west, and the B4518 road to its east, and has the town of Llanidloes towards the north.

When the original 400m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 435m summit height.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 40m of drop, based on the 435m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the 395m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. And these are the details the hill was listed by when the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013.

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

LIDAR summit image of Wenallt (SN 967 784)

LIDAR analysis gives the highest ground on this hill as 433.0m positioned at SN 96743 78468, and this 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 433.0m and this was derived from LIDAR analysis, this is 2.0m lower than the originally listed summit height, which was based on the 435m 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: Hirddywel

Name: Wenallt

OS 1:50,000 map: 136, 147

Summit Height (New Height): 433.0m (LIDAR)

Summit Grid Reference: SN 96743 78468 (LIDAR)

Bwlch Height: 394.0m (LIDAR)

Bwlch Grid Reference: SN 95366 78745 (LIDAR)

Drop: 39.0m (LIDAR)

Myrddyn Phillips and Aled Williams (October 2025)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Moel Wnog (SH 735 440) - 24th significant height revision

Hill Reclassifications post for Moel Wnog

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail produced by Joe Nuttall in his surface analysis progamme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Aled Williams and Myrddyn Phillips.

LIDAR image of Moel Wnog (SH 735 440)

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

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill now being listed in the 400m Sub-Pedwar category. The criteria for 400m Sub-Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Moel Wnog and it is adjoined to the Arenig Fach group of hills, which are situated in the north-westerly part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor road to its west, the A470 road farther to its west, the B4391 road to its south-west and the B4407 road to its south-east, and has the village of Ffestiniog towards the south-west.

When the original 400m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 29 of drop, based on an estimated c 468m summit height and an estimated c 439m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map.

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

Prior to the 1^st edition of the Y Pedwarau being published by Europeaklist in May 2013, the details for this hill were re-evaluated and it was listed as a Pedwar with an estimated c 34m of drop, based on the 473m summit spot height that appears on the Harvey 1:40,000 British Mountain Map and an estimated c 439m bwlch height.

LIDAR summit image of Moel Wnog (SH 735 440)

LIDAR analysis gives the highest ground on this hill as 471.3m positioned at SH 73522 44084, and this 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 471.3m and this was derived from LIDAR analysis, this is 3.3m higher than the originally listed estimated height of c 468m which was based on interpolation of the uppermost 460m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Arenig Fach

Name: Moel Wnog

OS 1:50,000 map: 124

Summit Height (New Height): 471.3m (LIDAR)

Summit Grid Reference: SH 73522 44084 (LIDAR)

Bwlch Height: 441.5m (LIDAR)

Bwlch Grid Reference: SH 73597 44355 (LIDAR)

Drop: 29.8m (LIDAR)

Myrddyn Phillips and Aled Williams (August 2023)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Ffridd Ddu (SH 726 064) - 23rd significant height revision

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales and Y Pellennig – The Remotest Hills of Wales, with the summit height, bwlch height and their locations, the drop, remoteness and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Ffridd Ddu (SH 726 064)

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

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being listed in the 400m Sub-Pedwar category. The criteria for 400m Sub-Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

Y Pellennig –The Remotest Hills of Wales - Welsh hills whose summit is at least 2.5km from the nearest paved public road and the hill has a minimum 15m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is available as a downloadable e-booklet or print-booklet version on Mapping Mountains Publications with the up-to-date master list available on Mapping Mountains to download in Google Doc format.

Y Pellennig - The Remotest Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Ffridd Ddu and it is adjoined to the Tarren y Gesail group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with the B4405 road to its north-west and the A487 road to its east, and has the town of Machynlleth towards the south.

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 20m of drop, based on the 433m summit spot height and the 413m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. These values also appeared for this hill when the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013 and the 1^st edition of Y Pellennig – The Remotest Hills of Wales was published by Europeaklist in April 2015.

Extract from the interactive mapping hosted on the WalkLakes website

One of the mapping resources now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme. This map has many spot heights not on other publicly available maps and for this hill it also shows a 433m summit spot height.

LIDAR summit image of Ffridd Ddu (SH 726 064)

LIDAR analysis gives the highest ground on this hill as 435.0m positioned at SH 72667 06467, and this 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 435.0m and this was derived from LIDAR analysis, this is 2.0m higher than the previously listed height of 435m which was based on the spot height that appeared on 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: Tarren y Gesail

Name: Ffridd Ddu

OS 1:50,000 map: 124

Summit Height (New Height): 435.0m (LIDAR)

Summit Grid Reference: SH 72667 06467 (LIDAR)

Bwlch Height: 413.0m (LIDAR)

Bwlch Grid Reference: SH 72593 06527 (LIDAR)

Drop: 22.0m (LIDAR)

Remoteness: 2.590km

Myrddyn Phillips and Aled Williams (July 2023)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Stonewall Hill (SO 318 696) - 22nd significant height revision

1st survey post for Stonewall Hill

2nd survey post for Stonewall Hill

Hill Reclassifications post for Stonewall Hill

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales under the classification of National Top status (for details relating to the concept of National Tops see separate post), with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams.

Stonewall Hill (SO 318 696)

The criteria for the list this height revision affects are:

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being included in the 400m Sub-Pedwar category. The criteria for 400m Sub-Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Stonewall Hill and it is adjoined to the Beacon Hill group of hills, which are situated in Mid and West Wales (Region B, Sub-Region B1), and it is positioned with the A4113 road to its north, a minor road to its immediate west and the B4355 road farther to its west, and has the town of Trefyclo (Knighton) towards the north-west.

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

When the original 400m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included as the concept of National Tops had not been devised. The hill was subsequently analysed using contemporary Ordnance Survey maps and LIDAR for height and drop. The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

LIDAR image of Stonewall Hill (SO 318 696)

LIDAR analysis confirms this hill as over 400m in height, and as the summit has now been surveyed with the Trimble GeoXH 6000, it is this result that is being prioritised for listing purposes and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated 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.

The Trimble GeoXH 6000 gathering data at the summit of Stonewall Hill

Therefore, this hill’s new listed summit height is 400.1m and this was derived from a Trimble GeoXH 6000 survey, this is 5.1m higher than the uppermost 395m ring contour taking in the summit of this hill on contemporary Ordnance Survey maps, although an erroneous 400m ring contour is shown toward the west.

The full details for the hill are:

Group: Beacon Hill

Name: Stonewall Hill

OS 1:50,000 map: 137, 148

Summit Height (New Height): 400.1m (converted to OSGM15)

Summit Grid Reference: SO 31823 69655

Bwlch Height: 376.4m (converted to OSGM15)

Bwlch Grid Reference: SO 31273 70279

Drop: 23.8m

Myrddyn Phillips and Aled Williams (October 2021)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Cefn Sarnau (SO 014 341) - 21st significant height revision

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales and Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips.

LIDAR image of Cefn Sarnau (SO 014 341)

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

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being listed in the 390m Sub-Pedwar category. The criteria for 390m Sub-Pedwar status being all Welsh hills at or above 390m and below 400m in height that have 20m or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

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

The name the hill is listed by is Cefn Sarnau and it is adjoined to the Mynydd Epynt group of hills, which are situated in the south-eastern part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the Afon Honddu and the B4520 road to its east, and has the small community of Capel Isaf (Lower Chapel) towards the north-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website the summit height of this hill was listed as c 390m which was based on the uppermost contour that appears on Ordnance Survey 1:25,000 Explorer maps.

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

When the P30 lists were standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 395m summit height, and these details were used when the hill was listed in the 1^st edition of the Y Pedwarau published by Europeaklist in May 2013.

LIDAR summit image of Cefn Sarnau

The summit height produced by LIDAR analysis is 397.6m and is positioned at SO 01415 34161, 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 listed summit height is 397.6m and this was derived from LIDAR analysis, this is 2.6m higher than the estimated c 395m summit height that was previously given for this hill.

The full details for the hill are:

Group: Mynydd Epynt

Name: Cefn Sarnau

OS 1:50,000 map: 160

Summit Height (New Height): 397.6m (LIDAR)

Summit Grid Reference: SO 01415 34161 (LIDAR)

Bwlch Height: 355.65m (LIDAR)

Bwlch Grid Reference: SO 01482 34779 (LIDAR)

Drop: 42.0m (LIDAR)

Myrddyn Phillips and Aled Williams (March 2020)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Grugfryn (SJ 248 356) - 20th significant height revision

Survey post for Grugfryn

Significant Name Changes post for Grugfryn

Summit Relocations post for Grugfryn

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m 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 Aled Williams.

Grugfryn (SJ 248 356)

The criteria for the list this height revision affects are:

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height with 30m minimum drop, the list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

The name of the hill is Grugfryn and it is adjoined to the Y Berwyn group of hills, which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is encircled by minor roads with the B4579 road to its south-west, and has the village of Glyn Ceiriog towards the west north-west.

When the original 400m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website the summit height of this hill was listed as 403m which was based on the spot height positioned at SJ 24849 35660 that appears on the Ordnance Survey 1:25,000 Explorer map.

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

The upper section of this hill is immersed in a conifer plantation and the 403m spot height appears adjacent to a forest track. This area was visited and a mound on the western side of the track was surveyed with the Trimble GeoXH 6000, resulting in a 404.05m height positioned at SJ 24842 35652.

The Trimble GeoXH 6000 gathering data from the mound beside the indistinct forest track

LIDAR summit image of Grugfryn

The summit height produced by LIDAR analysis is 405.1m positioned at SJ 24835 35615, 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 listed summit height is 405.1m and this was produced by LIDAR analysis, this is 2.1m higher than the 403m spot height that appears on contemporary Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Name: Grugfryn

OS 1:50,000 map: 126

Summit Height (New Height): 405.1m (LIDAR)

Summit Grid Reference: SJ 24835 35615 (LIDAR)

Bwlch Height: 361.9m (LIDAR)

Bwlch Grid Reference: SJ 24456 36336 (LIDAR)

Drop: 43.2m (LIDAR)

For details on the Trimble GeoXH 6000 survey of this hill

Myrddyn Phillips and Aled Williams (November 2019)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Esgair Llwyn Gwyn (SN 885 790) - 19th significant height revision

Survey post for Esgair Llwyn Gwyn

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived by LIDAR analysis conducted by Aled Williams and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

Approaching the summit of Esgair Llwyn Gwyn (SN 885 790)

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

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, the list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to the Mapping Mountains publication of this list appearing on the 30th January 2017, and the list is now available in its entirety on Mapping Mountains in Google Doc format.

The name the hill is listed by is Esgair Llwyn Gwyn and it is adjoined to the Y Garn group of hills, which are situated in the north-western part of South Wales (Region B, Sub-Region B1), and it is positioned with the Afon Gwy (River Wye) and the A44 road to its north and the Afon Gwy (River Wye) and the A470 road to its south-east, and has the village of Llangurig towards the east north-east.

When the original Welsh 400m P30 list was published on Geoff Crowder’s v-g.me website, this hill was listed with a 438m summit height, based on the spot height positioned at SN 88588 79070 that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

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

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

LIDAR image of Esgair Llwyn Gwyn (SN 885 790)

As this hill had now been surveyed with the Trimble GeoXH 6000, it is this result that is being prioritised for this hill and this summit height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Gathering data at the summit of Esgair Llwyn Gwyn

Gathering data at the bwlch of Esgair Llwyn Gwyn

Therefore, the new listed summit height of this hill is 435.9m and this was derived from a Trimble GeoXH 6000 survey. This is not a dramatic revision in height compared to some revised heights and is 2.1m lower than the previous listed height of 438m which was derived from the summit spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Group: Y Garn

Name: Esgair Llwyn Gwyn

OS 1:50,000 map: 135, 136, 147

Summit Height (New Height): 435.9m (converted to OSGM15)

Summit Grid Reference: SN 88577 79070

Bwlch Height: 402.3m (converted to OSGM15)

Bwlch Grid Reference: SN 88120 78849

Drop: 33.6m

Myrddyn Phillips and Aled Williams (November 2019)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Craig Celynnin (SH 746 733) - 18th significant height revision

Survey post for Craig Celynnin

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips which took place on the 22^nd May 2019.

Craig Celynnin (SH 746 733)

The criteria for the list this height revision applies to are:

Y Pedwarau – Welsh hills at or above 400m and below 500m in height that have a minimum 30m of drop, whilst the criteria for 400m Sub-Pedwar status are all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to the Mapping Mountains publication of this list appearing on the 30^th January 2017.

The name of the hill is Craig Celynnin 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 the north-east.

When the original Welsh 400m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 407m summit height, based on the spot height positioned at SH 746 733 that appears on the Ordnance Survey 1:25,000 Explorer map.

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

The summit height produced by the Trimble GeoXH 6000 survey is 404.8m, 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 Trimble GeoXH 6000 gathering data at the summit of Craig Celynnin

Therefore, this hill’s new listed summit height is 404.8m and this was produced by a Trimble GeoXH 6000 survey, this is 2.2m lower than its previously listed height of 407m that appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Carneddau

Name: Craig Celynnin

OS 1:50,000 map: 115

Summit Height (New Height): 404.8m (converted to OSGM15)

Summit Grid Reference: SH 74667 73373

Bwlch Height: 377.1m (converted to OSGM15)

Bwlch Grid Reference: SH 74604 73263

Drop: 27.7m (converted to OSGM15)

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

Myrddyn Phillips and Aled Williams (August 2019)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Fuches (SN 866 836) - 17th significant height revision

Survey post for Fuches

Hill Reclassifications post for Fuches

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau, with the summit height, drop and status of the hill confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips.

The criteria for the list this height revision applies to are:

The name of the hill is Fuches and it is adjoined to the Pumlumon range with its Cardinal Hill being Pumlumon Fawr (SN 789 869) and is placed in the Region of Mid and West Wales (Region B, Sub-Region B2). The hill is situated between the stream valleys of the Afon Hafren (River Severn) to the north-east and the Afon Gwy (River Wye) to the south, and has the small community of Llangurig towards the south-east.

Although the hill is a part of designated open access land it is also immersed in conifer plantation. However, the summit of the hill is easily reached via a wide path now used by trail riders that follows the summit ridge in a north-east to south-west direction, and this can be accessed from a forest track to the north-east of the summit.

When interpolated summit heights were added to the original Welsh P30 lists that were published on Geoff Crowder’s v-g.me website this hill was listed with an estimated c 453m summit height based on the area of its uppermost 450m contour ring on contemporary Ordnance Survey maps, this was only revised through LIDAR analysis which resulted in a summit height of 446.7m. However, the LIDAR height was queried as the whole hill is immersed in conifer plantation and this has become known to compromise the accuracy of some LIDAR values, and as the LIDAR value also affected this hill’s status, it was decided to survey the hill with the Trimble GeoXH 6000.

The summit height produced by the Trimble GeoXH 6000 survey is 449.3m (converted to OSGM15), this is not a dramatic height revision when considering its uppermost contour ring on contemporary Ordnance Survey maps, 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 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.

Therefore, this hill’s new summit height is 449.3m (converted to OSGM15) and this was produced by a Trimble GeoXH 6000 survey, this is 3.7m lower than its original estimated height of c 453m and 2.6m higher than the height produced by LIDAR analysis.

The full details for the hill are:

Group: Pumlumon

Name: Fuches

OS 1:50,000 map: 135, 136

Summit Height (New Height): 449.3m (converted to OSGM15)

Summit Grid Reference: SN 86623 83656

Drop: 30.2m (converted to OSGM15)

The Trimble set-up position at the summit of Fuches 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 and Aled Williams (September 2018)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Twyn y Waun (SO 085 065) - 16th significant height revision

Survey post for Twyn y Waun

Hill Reclassifications post for Twyn y Waun

There has been a Significant Height Revision to a summit of a hill that is now listed in the Y Pedwarau, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that confirmed this height revision being conducted on the 1^st December 2017.

The criteria for the list this height revision affects are:

Y Pedwarau – All Welsh hills at and above 400m and below 500m in height that have 30m minimum drop. Whilst the criteria for 400m Sub-Pedwar status are all Welsh hills at and above 400m and below 500m in height that have 20m or more and below 30m of drop.

The name of the hill is Twyn y Waun and this hill is the result of mine spoil from the Ffos-y-fran opencast mine, as a result it is considered a man-made hill. It is situated in the Y Cymoedd – dwyreiniol range of hills which are in the central part of South Wales (Region C, Sub-Region C2), and it is positioned between the town of Merthyr Tudful (Merthyr Tydfil) to its west and Rhymni (Rhymney) to its east.

As this man-made hill is a part of a working mine permission to visit should be sought, for those wishing to do so a public footpath leaves the convenience of a near minor road to the north north-east of the hill.

Prior to the survey with the Trimble GeoXH 6000 this man-made hill was not classified although it had been noted; most recently by Rob Woodall who reported its approximate height and prominence. This hill possesses no ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps with the continuation of contours from the unmined land to the east of the hill being between 400m – 410m high compared to where the summit of this man-made hill is now situated.

The resulting survey with the Trimble GeoXH 6000 produced a summit height of 460.5m (converted to OSGM15) and a bwlch height of 419.5m (converted to OSGM15), with these values giving this hill 41.0m of drop, with the summit height being a dramatic increase in height compared to the continuation of map contours from the unmined land to the east and therefore 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 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 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, the new height for this man-made hill 460.5m (converted to OSGM15), and as no contours exist for this hill on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps this is a dramatic 50.5m increase in height compared to the continuation of the 410m contour from the unmined land to the east of this hill.

The full details for the hill are:

Cardinal Hill: Twyn y Waun

Summit Height (New Height): 460.5m (converted to OSGM15)

Name: Twyn y Waun

OS 1:50,000 map: 160

Summit Grid Reference: SO 08549 06591

Drop: 41.0m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Twyn y Waun (SO 085 065) which resulted in this hill's significant height revision

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

Myrddyn Phillips and Aled Williams (January 2018)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Twyn y Waun (SO 082 070) - 15th significant height revision

Survey post for Twyn y Waun

There has been a Significant Height Revision to a summit of a hill that is now listed as a Dual Summit in the Y Pedwarau, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that confirmed this height revision being conducted on the 1^st December 2017.

The criteria for the list this height revision affects are:

A hill classified as a Dual Summit is defined as one which has an extant natural summit coupled with that of an artificial summit, which can be described as being stable in character. Twyn y Waun meets these criteria as it has an intact 450.6m natural summit at SO 08442 07378 and a 476.0m (converted to OSGM15) higher man-made summit at SO 08209 07041, and this article relates to the latter man-made summit.

The name of the hill is Twyn y Waun and it is situated in the Y Cymoedd – dwyreiniol range of hills which are in the central part of South Wales (Region C, Sub-Region C2), and the hill is positioned between the town of Merthyr Tudful (Merthyr Tydfil) to its west and Rhymni (Rhymney) to its east.

As this man-made hill is a part of a working mine permission to visit should be sought, however its summit is on the border of designated open access land shown on the Ordnance Survey 1:25,000 Explorer map, and for those wishing to visit a public footpath leaves the convenience of a near minor road to the east of the hill.

Prior to the survey with the Trimble GeoXH 6000 the man-made summit was not classified although it had been noted; most recently by Rob Woodall who reported its significant height difference when compared to the natural summit of Twyn y Waun. The man-made summit possesses no ring contour on Ordnance Survey maps with conflicting highest ring contours for the natural Dual Summit of Twyn y Waun of 430m on the 1:25,000 Explorer map and 450m on the 1:50,000 Landranger map and the Interactive Coverage Map hosted on the Geograph website. The resulting survey with the Trimble GeoXH 6000 produced a summit height of 476.0m (converted to OSGM15) which is a dramatic increase in height compared to map data and therefore comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, the new height for this man-made Dual Summit is 476.0m (converted to OSGM15), and as no contours exist for the upper part of this Dual Summit this is a dramatic 26m increase in height compared to the uppermost 450m contour on the Ordnance Survey 1:50,000 Landranger map and a 46m increase in height compared to the uppermost 430m contour on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Cardinal Hill: Twyn y Waun

Summit Height (New Height): 476.0m (converted to OSGM15) for man-made Dual Summit

Name: Twyn y Waun

OS 1:50,000 map: 160

Summit Grid Reference: SO 08209 07041

Drop: 96.0m (Trimble GeoXH 6000 summit and LIDAR bwlch) for man-made Dual Summit

The Trimble GeoXH 6000 gathering data at the man-made Dual Summit of Twyn y Waun (SO 08209 07041) which resulted in this summit's significant height revision

For details on the survey that significantly revised the height of this Dual Summit

Myrddyn Phillips and Aled Williams (January 2018)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Pawl Hir (SO 101 595) - 14th significant height revision

Survey post for Pawl Hir

Summit Relocation post for Pawl Hir

There has been a Significant Height Revision to a hill that was surveyed for 400m Sub-Pedwar status with the Trimble GeoXH 6000, with the survey that resulted in this significant height revision taking place on the 3^rd October 2017 in good, clear conditions.

The criteria for the list this hill was surveyed for are:

Y Pedwarau – All Welsh hills at or above 400m and below 500m in height that have 30m minimum drop. Whilst the criteria for 400m Sub-Pedwar status is all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.

The name of the hill is Pawl Hir and it is situated in the Fforest Glud range of hills which are in the eastern part of Mid and West Wales (Region B, Sub-Region B1), and the hill is positioned between the town of Llandrindod (Llandrindod Wells) to its west north-west and the small community of Hundred House to its south.

Pawl Hir (SO 101 595)

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 public footpath crosses the hill from a west – east direction and just bi-passes the two high points of the hill, one of which is situated on the northern part of the summit area and the other on the southern part, with the easiest and most convenient ascent being from the east following the footpath up the hill from the convenience of a sharp corner on a minor lane, where there is adequate parking for a car.

Prior to the survey with the Trimble GeoXH 6000 the hill was noted with 19m of drop based on the 408m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and the 389m bwlch spot height that appears on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website, this latter map also gives a 407m spot height to the south south-west of the 408m summit spot height. Therefore, the purpose of the survey was to ascertain the high point of the hill and determine if it had the minimum of 20m of drop required to be classified as a 400m Sub-Pedwar.

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

In all four points were surveyed for the high point of this hill; one on the northerly land where the 408m spot height appears and three on the southerly land where the 407m spot height appears, these results are given below:

1^st survey, 408m spot height – 404.903m (converted to OSGM15) at SO 10225 59703

2^nd survey, 407m spot height – 405.785m (converted to OSGM15) at SO 10108 59510

3^rd survey, 407m spot height – 405.359m (converted to OSGM15) at SO 10036 59429

4^th survey, 407m spot height – 405.641m (converted to OSGM15) at SO 10027 59400

Although the three survey results obtained on the southerly high point of this hill do not come within the parameters of the Significant Height Revisions used within this page heading, the survey result obtained on the northerly high point does, and therefore this is worth recording, these parameters are:

The highest height obtained with the Trimble GeoXH 6000 compared to where each spot height appears on the ground is given below:

408m spot height - 404.903m (converted to OSGM15) at SO 10225 59703

407m spot height – 405.785m (converted to OSGM15) at SO 10108 59510

Although the position where the 408m spot height appears on the ground is not the high point of the hill, the result produced by the Trimble GeoXH 6000 for this position does come within the above parameters.

Therefore, this hill’s new summit height is 405.8m (converted to OSGM15) which is positioned on the southerly land of this hill’s summit area, whilst the 404.9m (converted to OSGM15) surveyed height which is positioned on the northerly land of this hill’s summit area is 3.1m lower than the Ordnance Survey 408m spot height that appears on the 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Cardinal Hill: Gilwern Hill

Summit Height (New Height): 405.8m (converted to OSGM15)

Name: Pawl Hir

OS 1:50,000 map: 148

Summit Grid Reference: SO 10108 59510

Drop: 16.9m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the northerly high point of this hill which resulted in this point's significant height revision

For details on the survey that ascertained an accurate summit height for this hill

Myrddyn Phillips and Aled Williams (December 2017)

Mapping Mountains - Significant Height Revisions - Y Pedwarau - The 400m Hills of Wales

Mynydd Epynt (SN 961 464) - 13th 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 - The 400m Hills of Wales and the 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. With the change in the listed summit height initiated by LIDAR analysis conducted by Aled Williams.

Mynydd Epynt (SN 961 464)

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

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Mynydd Epynt, and it is adjoined to its own group of hills; Mynydd Epynt, which are situated in the central part of South Wales (Region C2, Sub-Region C2A), and it is positioned with the B4519 road to its north-east, and has the town of Llanfair-ym-Muallt (Builth Wells) towards the north-east.

When the original 400m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a summit height of 478m, 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

However, it was not until LIDAR became available and the subsequent Trimble GeoXH 6000 survey 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 Mynydd Epynt (SN 961 464)

The summit height produced by the Trimble GeoXH 6000 is 475.7m positioned at SN 96124 46428, 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 at the summit of Mynydd Epynt (SN 961 464)

Therefore, the new listed summit height of this hill is 475.7m and this was derived from a Trimble GeoXH 6000 survey, this is 2.3m lower than the previously listed summit height, which was based on the 478m 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: Mynydd Epynt

Name: Mynydd Epynt

OS 1:50,000 map: 147

Summit Height (New Height): 475.7m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference: SN 96124 46428 (Trimble GeoXH 6000)

Bwlch Height: 277.9m (LIDAR)

Bwlch Grid Reference: SN 84054 43300 (LIDAR)

Drop: 197.8m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance: 41.58% (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips and Aled Williams (January 2017)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Moelfre (SH 717 744) - 12th significant height revision

Survey post for Moelfre

Hill Reclassifications post for Moelfre

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill listed in the Y Pedwarau, and which was subsequently confirmed by LIDAR analysis conducted by Aled Williams, with the survey that resulted in this height revision being conducted on the 4^th July 2016.

LIDAR image of Moelfre (SH 717 744)

The criteria for the listing that this height revision affects are:

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

400m Sub- Pedwarau - Welsh hills at and above 400m and below 500m in height that have 20m or more and below 30m of drop.

The name of the hill is Moelfre and it is situated in the Carneddau range of hills which are in north-west Wales. This hill range comprises some of the highest mountains in the country but the evening walk when the survey was conducted concentrated on some of its 300m and 400m lower hills.

Moelfre is positioned above the towns of Penmaenmawr which is to its north and Llanfairfechan which is to its west and it can be easily accessed from a green track that continues from the end of a minor lane to the hill’s west, or from its north-west where public footpaths and bridleways lead close to its summit.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 435m, with this height taken from the Ordnance Survey 1:50,000 Landranger map, Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey enlarged mapping hosted on the Geograph website. The 435m height seems to be a recent addition as the series of Ordnance Survey Six-Inch maps from 1888 - 1946 have a 1,422ft (433.4m) height, whilst the Ordnance Survey Seventh Series One-Inch map and the Historical 1:25,000 map has 1,423ft (433.7m).

Moelfre was surveyed with the Trimble GeoXH as being 433.0m (converted to OSGM15) high. 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 is easily identified and consists of an ancient cairn that is now an oval mound, with the centre of the mound being slightly hollowed, and therefore this hill’s new summit height as surveyed by the Trimble GeoXH 6000 is 433.0m (converted to OSGM15) which is 2.0m lower than its previously listed height of 435m which appears on the Ordnance Survey enlarged mapping hosted on the Geograph website and the 1:25,000 Explorer and 1:50,000 Landranger maps.

The full details for the hill are:

Cardinal Hill: Tal y Fan

Summit Height: 433.0m (converted to OSGM15)

Name: Moelfre

OS 1:50,000 map: 115

Summit Grid Reference: SH 71733 74418

Drop: 18.3m (Trimble summit and LIDAR bwlch)

The Trimble GeoXH 6000 gathering data at the summit of Moelfre (SH 717 744) 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 and Aled Williams (August 2016)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Clip yr Orsedd (SH 711 747) - 11th significant height revision

Survey post for Clip yr Orsedd

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill that is listed in the Y Pedwarau, with the survey that resulted in this height revision being conducted on 14^th July 2016. The criteria for Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 30m minimum drop.

The name of the hill is Clip yr Orsedd and it is situated in the northern part of the Carneddau range of hills which is in north-west Wales. This hill range comprises some of the highest mountains in the country but the evening walk when the survey was conducted concentrated on some of its lower hills.

The hill is positioned above the towns of Llanfaifechan which is to its west and Penmaenmawr which is to its north north-east and it can be easily accessed from a green track that continues from the end of a minor lane to the hill’s west. An alternative route is via part of the Wales Coast Path, with both routes just bi-passing the summit to its south.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 429m, with this height taken from the Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey enlarged mapping hosted on the Geograph website.

The summit of Clip yr Orsedd was surveyed with the Trimble GeoXH 6000 as being 426.6m (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:

The summit of this hill is easily identified and consists of an outcrop of rock close to the ground and therefore this hill’s new summit height as surveyed by the Trimble GeoXH 6000 is 426.6m (converted to OSGM15) which is 2.4m lower than its previously listed height of 429m which appears on the Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey enlarged mapping hosted on the Geograph website.

The full details for the hill are:

Cardinal Hill: Tal y Fan

Summit Height: 426.6m (converted to OSGM15, Trimble GeoXH 6000)

Name: Clip yr Orsedd

OS 1:50,000 map: 115

Summit Grid Reference: SH 71185 74743 (Trimble GeoXH 6000)

Drop: 39.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

The Trimble GeoXH 6000 gathering data at the summit of Clip yr Orsedd (SH 711 747) 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 and Aled Williams (August 2016)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Penmaen Mawr (SH 698 755) - 10th significant height revision

Survey post for Penmaen Mawr

Hill Reclassifications post for Penmaen Mawr

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill that is listed in the Y Pedwarau and the Y Trichant, with the survey that resulted in this height revision being conducted on the 14^th July 2016.

The criteria for the 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. 300m Double Sub- Pedwarau - Welsh hills at and above 390m and below 400m in height that have 20m or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams.

Y Trichant - Welsh hills at and above 300m and below 400m in height that have 30m minimum drop. Sub-Trichant - Welsh hills at and above 300m and below 400m in height that have 20m or more and below 30m of drop. The list is authored by Myrddyn Phillips and the Introduction to the list and its re-naming has been published on Mapping Mountains.

The hill is named Penmaen Mawr and it is situated in the Carneddau range of hills, and is positioned above and to the immediate south of the busy A 55 as it heads westward between the towns of Penmaenmawr and Llanfairfechan, which are situated to the hill’s east and west respectively.

The summit area of Penmaen Mawr has been quarried, and prior to the first quarry opening in 1830 and the subsequent resulting expansion of operations the hill was substantially higher, with a 1,550ft (472m) map height given it on the Ordnance Survey Popular and New Popular One-Inch maps, with this height also appearing on the Ordnance Survey Six-Inch map published in 1888.

The quarrying of this hill has created two summits with a gaping hole between, the westerly summit is higher than the easterly, although the latter is more impressive due to a shear rock face leading toward its high point. Each summit is listed by the same name of Penmaen Mawr as they are both a part of the hill that is known by this name, and their height data is given below:

Penmaen Mawr: 390.4m (converted to OSGM15, Trimble GeoXH 6000) at SH 69865 75523

Penmaen Mawr: 385.8m (LIDAR data) at SH 70292 75649

Over recent years the summit area of this hill has appeared without any uppermost contour lines as is the norm for quarried ground that is represented on Ordnance Survey maps, with the highest contour being 370m which appears on the upper western part of this hill.

Therefore this hill’s new summit height is 390.4m (converted to OSGM15) which is 20.4m higher than its uppermost contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill: Tal y Fan

Summit Height: 390.4m (converted to OSGM15)

Name: Penmaen Mawr

OS 1:50,000 map: 115

Summit Grid Reference: SH 69865 75523

Drop: 26.9m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data 0.39m above the summit of Penmaen Mawr (SH 698 755) 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 and Aled Williams (July 2016)

Mapping Mountains - Significant Height Revisions - Y Pedwarau - The 400m Hills of Wales

Craig y Garreg Lwyd (SH 730 427) - 9th significant height revision

Survey post for Craig y Garreg Lwyd

1st Hill Reclassifications post for Craig y Garreg Lwyd

2nd Hill Reclassifications post for Craig y Garreg Lwyd

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Leica GS15 survey conducted by John Barnard and Graham Jackson.

Craig y Garreg Lwyd (SH 730 427)

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

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills, with this hill being re-instated from 400m Sub-Pedwar status. The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Craig y Garreg Lwyd, and it is adjoined to the Arenig Fach group of hills, which are situated in the central part of North Wales (Region C1, Sub-Region C1A), and it is positioned with a minor road to its north-west, the B4391 road to its south and the B4407 road to its east, and has the village of Ffestiniog towards the west south-west.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips was published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a non-interpolated c 470 summit height, with its inclusion based on a basic levelling survey conducted by Myrddyn Phillips, resulting in 99ft/30.2m of drop.

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 35m of drop, based on the 478m summit spot height and the 443m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, and these are the details given the hill when the 1^st edition of the Y Pedwarau, now co-authored by Myrddyn Phillips and Aled Williams was published by Europeaklist in May 2013.

However, it was not until the Leica GS15 survey that its listed summit height was ascertained. This survey gives the highest ground on this hill as 473.8m positioned at SH 73043 42743, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 473.8m and this was derived from a Leica GS15 survey, this is 4.2m lower than the previously listed summit height, which was based on the 478m spot height that appeared 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: Arenig Fach

Name: Craig y Garreg Lwyd

OS 1:50,000 map: 124

Summit Height (New Height): 473.8m (converted to OSGM15)

Summit Grid Reference: SH 73043 42743

Bwlch Height: 443.6m (converted to OSGM15)

Bwlch Grid Reference: SH 73220 42799

Drop: 30.2m

Myrddyn Phillips and Aled Williams (March 2016)

Mapping Mountains - Significant Height Revisions - Y Pedwarau - The 400m Hills of Wales

Y Drum (SH 735 428) - 8th significant height revision

Survey post for Y Drum

Summit Relocations post for Y Drum

Significant Name Changes post for Y Drum

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips initiated by an on-site inspection conducted by Aled Williams.

Y Drum (SH 735 428)

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

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills; 500m Sub-Pedwarau, 500m Double Sub-Pedwarau, 400m Sub-Pedwarau, 390m Sub-Pedwarau and the 390m Double Sub-Pedwarau. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Y Drum, and this was derived from local and historical information with research conducted by Aled Williams, and it is adjoined to the Arenig Fach group of hills, which are situated in the central part of North Wales (Region C1, Sub-Region C1A), and it is positioned with the B4391 road to its south and the B4407 road to its east, and has the village of Ffestiniog towards the west south-west.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips was published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 479m summit height positioned at SH 733 428, with the caveat that the four small 480m ring contours just to the north-east and east had been missed.

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

After the sub list was standardised and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 35m of drop, based on an estimated c 482m summit height and an estimated c 447m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map.

When the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013 the details for this hill were re-evaluated and it was listed with a 486m summit height, based on the spot height that appears on the Harvey 1:40,000 British Mountain Map to Eryri/Snowdonia and which is positioned in the vicinity of the most northerly of the 480m ring contours that appear on the Ordnance Survey 1:25,000 Explorer map, with the high point of this contour ring positioned at SH 73542 42903.

Extract from the Harvey 1:40,000 British Mountain Map to Eryri/Snowdonia

The position of the listed summit of this hill was subsequently moved to SH 73541 42812 after an on-site inspection by Aled Williams. However, it was not until the survey with the Trimble GeoXH 6000 that the details for this hill could be accurately re-assessed.

The new summit position of Y Drum is highlighted in yellow, with the old position of the summit highlighted in red. Photo: Aled Williams

This summit relocation was later confirmed by the Trimble GeoXH 6000 with the highest ground on this hill surveyed as 483.574m positioned at SH 73541 42812, whilst the position of the 486m Harvey spot height at SH 73542 42903 was surveyed as 482.686m, 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 at the new summit position of Y Drum (SH 735 428)

Therefore, the new listed summit height of this hill is 483.6m and this was derived from a Trimble GeoXH 6000 survey, this is 2.4m lower than the previously listed summit height, which was based on the 486m spot height that appears on the Harvey 1:40,000 British Mountain Map to Eryri/Snowdonia

The full details for the hill are:

Group: Arenig Fach

Name: Y Drum

OS 1:50,000 map: 124

Summit Height (New Height): 483.6m (converted to OSGM15)

Summit Grid Reference: SH 73541 42812

Bwlch Height: 449.2m (converted to OSGM15)

Bwlch Grid Reference: SH 73778 42825

Drop: 34.4m

Myrddyn Phillips and Aled Williams (March 2016)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Cwm Cynnydd Bank (SO 061 726) - 7th significant height revision

Survey post for Cwm Cynnydd Bank

Significant Name Changes post for Cwm Cynnydd Bank

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau that was initiated by a survey with the Trimble GeoXH 6000, with the survey that resulted in this height revision being conducted on 18^th February 2016. The criteria for Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 30m minimum drop.

The name of the hill is Cwm Cynnydd Bank and it is situated in the hills of the Pegwn Mawr range which is positioned in mid Wales and the survey was conducted during a walk taking in one Trichant and three Pedwar hills.

The hill is situated in woodland, but can be accessed from open hillside and forest tracks to within a few metres of its summit, which is positioned in mature conifer plantation just to the north of a broad path. The hill is situated to the north of the small community of Abaty Cwm Hir (Abbey Cwmhir) and to the south-east of the small community of Bwlch y Sarnau.

Prior to the survey with the Trimble GeoXH 6000 the hill was listed as a Pedwar with a 450m summit height taken the spot height that appears on the Ordnance Survey 1:50,000 Landranger map. This height equates to the old imperial height of 1,477ft that appears on the Ordnance Survey 1:25,000 Historical Map which originates from the series of Ordnance Survey old Six-Inch maps. This height appears near to or on the broad path that gives access to this hill’s summit and which traverses its broad north-east to south-west ridge.

When surveying this summit I waited a long time for the Trimble GeoXH 6000 to attain its 0.1m accuracy level before data should be logged, during this time I assessed the lay of land around the summit and tried to keep warm. I estimated the summit of the hill to be approximately 3m higher than the path where the centralised imperial height appears on the old Six-Inch map.

Therefore this hill’s new summit height is 454.9m (converted to OSGM15) which is 4.9m higher than its previously listed height of 450m and 14.9m higher than the uppermost 440m ring contour that appears on Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill: Brondre-fawr Hill

Summit Height: 454.9m (converted to OSGM15)

Name: Cwm Cynnydd Bank

OS 1:50,000 map: 136, 147

Summit Grid Reference: SO 06116 72668

Drop: 83.9m (converted to OSGM15)

Gathering data at the summit of Cwm Cynnydd Bank (SO 061 727) 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 and Aled Williams (February 2016)

Mapping Mountains - Significant Height Revisions - Y Pedwarau - The 400m Hills of Wales

Creigiau Cyrddau (SH 929 428) - 6th significant height revision

Survey post for Creigiau Cyrddau

Summit Relocations post for Creigiau Cyrddau

Significant Name Changes post for Creigiau Cyrddau

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams.

Creigiau Cyrddau (SH 929 428)

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

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is now listed by is Creigiau Cyrddau, and it is adjoined to the Carnedd y Filiast group of hills, which are situated in the central part of North Wales (Region C1, Sub-Region C1A), and it is positioned with the B4501 road to its north and west and a minor road and the A4212 road and the A494 road to south, and has the town of Y Bala towards the south.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips was published on Geoff Crowder’s v-g.me website, this hill was included in the accompanying Hills to be surveyed sub list with a 497m summit height, based on the spot height that appears at SH 93067 42836 on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 28m of drop, based on the 497m summit spot height and the 469m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map. And these are the details the hill was listed by when the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013.

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online. This mapping had many spot heights not on other publicly available Ordnance Survey maps and for this hill it had a 495m spot height positioned at SH 92974 42817.

Extract from the interactive mapping hosted on the WalkLakes website

The 495m spot height also appears on the WalkLakes interactive map that was originated from the Ordnance Survey Open Data programme. Another resource now available online is the interactive mapping hosted on the Welsh Government website and entitled the DataMapWales. This mapping has 5m contours and its detail matches that produced from the OS Terrain 5 product, which compliments much of that produced from LIDAR. This mapping also gives a 495m summit spot height.

Extract from the DataMapWales

However, it was not until the Trimble GeoXH 6000 survey that the details for this hill could be accurately re-assessed. The high point of the land where the 497m and the 495m spot heights appear on the ground were each surveyed with the following results:

497m spot height: 490.8m (converted to OSGM15) at SH 93066 42834

495m spot height: 494.6m (converted to OSGM15) at SH 92971 42820

The Trimble GeoXH 6000 survey gives the highest ground on this hill as 494.6m positioned at SH 92971 42820, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Gathering data on the new listed summit position of Creigiau Cyrddau with Aled wearing a red top standing on the old listed summit position

Therefore, the new listed summit height of this hill is 494.6m and this was derived from a Trimble GeoXH 6000 survey, this is 2.4m lower than the previously listed summit height, which was based on the 497m 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: Carnedd y Filiast

Name: Creigiau Cyrddau

OS 1:50,000 map: 125

Summit Height (New Height): 494.6m (converted to OSGM15)

Summit Grid Reference: SH 92971 42820

Bwlch Height: 468.5m (converted to OSGM15)

Bwlch Grid Reference: SH 93203 42714

Drop: 26.0m

Myrddyn Phillips and Aled Williams (October 2015)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Bryn Serth (SO 148 109) - 5th significant height revision

Survey post for Bryn Serth

Hill Reclassifications post for Bryn Serth

Summit Relocations post for Bryn Serth

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau that was initiated by a survey with the Trimble GeoXH 6000 and subsequently confirmed via LIDAR analysis conducted by Aled Williams, with these details being retrospective as the Trimble survey that resulted in this height revision was conducted on 12^th August 2015. The hill appeared in the listing of Y Pedwarau as a Pedwar with c 34m of drop and was reclassified to a 400m Sub-Pedwar due to the survey with the Trimble GeoXH 6000.

The criteria for Pedwar status is all Welsh hills at or above 400m and below 500m in height that have 30m minimum drop. Whilst the criteria for 400m Sub-Pedwar status is all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.

The name of the hill is Bryn Serth and it is situated in the hill range known as Cymoedd Gwent which is positioned in south Wales, and the survey was conducted during a walk in the company of Mark Trengove who had suggested visiting the hill.

Bryn Serth is situated on the northern outskirts of Tredegar at the head of the Cwm Sirhywi (Sirhowey Valley) and it can be easily accessed from a car park beside the busy A4047 which is positioned south-east of the summit. This car park also gives access to the Aneurin Bevan Memorial Stones; these consist of four monoliths and are set against the landscape of Ebbw Vale, Tredegar and Rhymney which form the constituencies which Aneurin Bevan represented during his years in Westminster.

Prior to the survey with the Trimble GeoXH 6000 the hill was listed as a Pedwar with its summit height estimated as c 410m based on a small uppermost 410m ring contour that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps. However, this point is not the high point of the hill as land approximately 100 metres further north was surveyed with the Trimble as being 2.0m higher than the position where the uppermost contour ring appears on the ground.

The two points surveyed with the Trimble GeoXH 6000 gave results that are significantly lower than current Ordnance Survey map data, these results are:

Northern summit: 403.927m (converted to OSGM15) at SO 14794 10908

Southern summit: 401.890m (converted to OSGM15) at SO 14782 10809

It is the southern summit where the small 410m ring contour appears on contemporary Ordnance Survey maps.

Since processing the data sets from this survey Aled has scrutinised on-line mapping and found that the Ordnance Survey Six-Inch map has a 1,327ft (404.47m) height on the area of the summit and a 1,242.5ft (378.71m) height on the area of the bwlch. These Six-Inch map values give Bryn Serth a drop of 25.76m which is comparable to the result produced by the Trimble GeoXH 6000 and by LIDAR analysis.

Therefore, this hill’s new summit height is 404.0m and this was derived from LIDAR analysis, and thus is 6m lower than its previously estimated height of c 410m and its uppermost ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Group: Cymoedd Gwent

Summit Height (New Height): 404.0m (LIDAR)

Name: Bryn Serth

OS 1:50,000 map: 161

Summit Grid Reference: SO 14807 10929 (LIDAR)

Drop: 25.8m (LIDAR)

Gathering data at the summit of Bryn Serth 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 and Aled Williams (September 2015)

Mapping Mountains - Significant Height Revisions - Y Pedwarau - The 400m Hills of Wales

Mynydd Poeth (SH 953 513) - 4th significant height revision

Survey post for Mynydd Poeth

Hill Reclassifications post for Mynydd Poeth

Summit Relocations post for Mynydd Poeth

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey and subsequent LIDAR analysis conducted by Myrddyn Phillips.

Mynydd Poeth (SH 953 513)

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

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being reclassified from the 400m Sub-Pedwar category. The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Mynydd Poeth and it is adjoined to the Mynydd Hiraethog group of hills, which are situated in the northern part of North Wales (Region C1, Sub-Region C1A), and it is positioned with minor roads to its west and south, and the B4501 road to its east, and has the village of Cerrigydrudion towards the south.

When the original 400m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 category.

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 29m of drop, based on the 417m summit spot height positioned at SH 95403 51069 that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and an estimated c 388m bwlch height, based on interpolation of 10m contouring between 390m – 400m, and these are the values given this hill when the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013.

The Trimble GeoXH 6000 gathering data at the summit of Mynydd Poeth

However, it was not until the Trimble GeoXH 6000 survey and when LIDAR became available that the details for this hill could be accurately re-assessed. The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

The Trimble GeoXH 6000 survey gives the highest ground on this hill as 419.3m positioned at SH 95375 51301, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

LIDAR image of Mynydd Poeth (SH 953 513)

Therefore, the new listed summit height of this hill is 419.3m and this was derived from a Trimble GeoXH 6000 survey, this is 2.3m higher than the previously listed summit height, which was based on the 417m spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group: Mynydd Hiraethog

Name: Mynydd Poeth

OS 1:50,000 map: 116

Summit Height (New Height): 419.3m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference: SH 95375 51301 (Trimble GeoXH 6000)

Bwlch Height: 387.3m (LIDAR)

Bwlch Grid Reference: SH 95072 51340 & SH 95070 51331 (LIDAR)

Drop: 33.0m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips and Aled Williams (August 2015)

Mapping Mountains - Significant Height Revisions - Y Pedwarau

Bryn Melyn (SO 109 184) - 3rd significant height revision

Survey post for Bryn Melyn

There has been a Significant Height Revision to a hill listed in the Y Pedwarau initiated from a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted on the 22^nd July 2014. With the criteria for Pedwar status being all Welsh hills at or above 400m and below 500m in height that have a minimum 30m of drop.

The name of the hill is Bryn Melyn and it is situated in the Bannau Brycheiniog (Brecon Beacons) range of hills in south Wales, with the survey of the hill conducted in the company of Mark Trengove who had suggested the walk.

Bryn Melyn can be easily accessed from the end of a minor road above the waters of the Talybont Reservoir which is situated in Glyn Collwn. The hill can also be accessed from its opposing valley of Dyffryn Crawnon which gives a slightly more rewarding and lengthy walk.

This hill's summit height has been increased from its current Ordnance Survey map height, as prior to the survey with the Trimble GeoXH 6000 the hill was listed with an estimated summit height of c 446m based on it having an uppermost contour ring of 440m on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps. Its new summit height is 450.5m (converted to OSGM15) which is 4.6m higher than its previously estimated height and 10.5m higher than its uppermost ring contour on current Ordnance Survey maps.

The full details for the hill are:

Cardinal Hill: Pen y Fan

Summit Height (New Height): 450.5m (converted to OSGM15)

Name: Bryn Melyn

OS 1:50,000 map: 161

Summit Grid Reference: SO 10941 18432

Drop: 38.2m (Trimble summit and LIDAR bwlch)

Gathering data from the summit of Bryn Melyn 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 and Aled Williams (August 2015)

Mapping Mountains - Significant Height Revisions - Y Pedwarau - The 400m Hills of Wales

Craig y Ganllwyd (SH 707 258) - 2nd significant height revision

Survey post for Craig y Ganllwyd

Hill Reclassifications post for Craig y Ganllwyd

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips.

Craig y Ganllwyd (SH 707 258)

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

Y Pedwarau – The 400m Hills of Wales. Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main list are five categories of sub hills, with this hill being reclassified from the 400m Sub-Pedwar category. The criteria for this sub category being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Craig y Ganllwyd, and it is adjoined to the Y Llethr group of hills, which are situated in the western part of North Wales (Region C1, Sub-Region C1A), and it is positioned with a minor road to its south-east, and the A470 road to its east, and has the village of Llanelltyd towards the south.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips was published on Geoff Crowder’s v-g.me website, this hill was included in the accompanying Hills to be surveyed sub list, with a non-interpolated c 420 summit height, with an accompanying note stating: 1:50000 and 1:25000 maps differ.

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 21m of drop, based on an estimated c 418m summit height and the 397m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

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

The details for this hill were re-evaluated when the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013 and it was subsequently listed with 26m of drop, based on the 423m summit spot height that appears on Harvey maps and the aforementioned 397m bwlch spot height.

However, it was not until the Trimble GeoXH 6000 survey that an accurate summit height could be given this hill.

The Trimble GeoXH 6000 gathering data at the summit of Craig y Ganllwyd

The Trimble GeoXH 6000 survey gives the highest ground on this hill as 430.9m positioned at SH 70775 25853, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Another resource now available online is the interactive mapping hosted on the Welsh Government website and entitled the DataMapWales. This mapping has 5m contours and its detail matches that produced from the OS Terrain 5 product, which compliments much of that produced from LIDAR. And for this hill this mapping shows the 415m, 420m, 425m and the uppermost 430m ring contour that is missing from the contemporary Ordnance Survey 1:25,000 Explorer map.

Extract from the DataMapWales

Therefore, the new listed summit height of this hill is 430.9m and this was derived from a Trimble GeoXH 6000 survey, this is 20.9m higher than the uppermost 410m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map and 7.9m higher than the previously listed summit height of 423m that appears as a spot height on Harvey maps. With the caveat that the Ordnance Survey 1:50,000 Landranger map has an uppermost 430m contour ring which compliments detail on the 1:2,500 base map which has an imperial height of 1,411ft (430m).

The full details for the hill are:

Group: Y Llethr

Name: Craig y Ganllwyd

OS 1:50,000 map: 124

Summit Height (New Height): 430.9m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference: SH 70775 25853 (Trimble GeoXH 6000)

Bwlch Height: 398.0m (LIDAR)

Bwlch Grid Reference: SH 70467 25923 (LIDAR

Drop: 32.9m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Myrddyn Phillips and Aled Williams (August 2015)

Mapping Mountains - Significant Height Revisions - Y Pedwarau - The 400m Hills of Wales

Craig y Derlwyn (SH 702 259) - 1st significant height revision

Survey post for Craig y Derlwyn

Hill Reclassifications post for Craig y Derlwyn

Craig y Derlwyn (SH 702 259)

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

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Craig y Derlwyn, and it is adjoined to the Y Llethr group of hills, which are situated in the western part of North Wales (Region C1, Sub-Region C1A), and it is positioned with a minor road to its south-east, and the A470 road to its east, and has the village of Llanelltyd towards the south.

When the original 400m height band of Welsh P30 hills compiled by Myrddyn Phillips was published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 22m of drop, based on an estimated c 428m summit height and an estimated c 406m bwlch height, with both heights based on interpolation of 10m contouring that appear on the Ordnance Survey 1:25,000 Explorer map. And these are the details the hill was listed by when the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013.

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

However, it was not until the Trimble GeoXH 6000 survey for the summit height and bwlch height, drop and therefore its status that the details for this hill could be accurately re-assessed.

Gathering data at the summit of Craig y Derlwyn

The Trimble GeoXH 6000 survey gives the highest ground on this hill as 430.8m positioned at SH 70245 25934, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Another resource now available online is the interactive mapping hosted on the Welsh Government website and entitled the DataMapWales. This mapping has 5m contours and its detail matches that produced from the OS Terrain 5 product, which compliments much of that produced from LIDAR. And for this hill this mapping shows the 430m uppermost ring contour that is missing from the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

Extract from the DataMapWales

Therefore, the new listed summit height of this hill is 430.8m and this was derived from a Trimble GeoXH 6000 survey, this is 10.8m higher than the uppermost 420m ring contour on the Ordnance Survey 1:25,000 Explorer map and 2.8m higher than the previously listed summit height of c 428m.

The full details for the hill are:

Group: Y Llethr

Name: Craig y Derlwyn

OS 1:50,000 map: 124

Summit Height (New Height): 430.8m (converted to OSGM15)

Summit Grid Reference: SH 70245 25934

Bwlch Height: 405.5m (converted to OSGM15)

Bwlch Grid Reference: SH 69837 26137

Drop: 25.3m

Myrddyn Phillips and Aled Williams (August 2015)

Monday, 23 October 2017

Mapping Mountains – Significant Height Revisions – Y Pedwarau - The 400m Hills of Wales

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