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

Welsh Highlands - Uchafion Cymru – Significant Height Revisions

The list to the Welsh Highlands - Uchafion Cymru comprise all Welsh hills at or above 500m in height with 15m minimum drop. Accompanying the main P15 list are three sub lists; these are the 500m Subs, 490m Subs and the Double Subs with their criteria detailed in the respective Change Registers available on Mapping Mountains. With details to this list given in the Introduction that was published on Mapping Mountains in November 2015.

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 P15 list and the sub lists appear below presented chronologically in receding order.

Postscript: On the 7^th January 2023 it was announced that the sub hills accompanying the main listing of the Welsh Highlands – Uchafion Cymru now take in just one category, this category is entitled the Welsh Highland Subs. The criteria for which are all Welsh hills at and above 500m in height with 10m or more and below 15m of drop.

Therefore, the 490m Subs and 490m Double Subs have been dispensed with and the criteria for the 500m Subs that included Welsh hills with 14m or more and below 15m of drop, have been amended to include Welsh hills with 10m or more and below 15m of drop and their title changed to the Welsh Highland Subs.

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Foel Ganol (SH 687 715) - 35th significant height revision

There has been a Significant Height Revision to a hill that is listed in the 500m Twmpau and the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams.

LIDAR image of Foel Ganol (SH 687 715)

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

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with an accompanying sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or above 500m and below 600m in height that have 20m or more and below 30m of drop. With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips and is published on Mapping Mountains in Google Doc format.

500m Twmpau by Myrddyn Phillips

Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop. This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The name the hill is listed by is Foel Ganol and it is adjoined to the Carnedd Llywelyn 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 to its north-west and a minor road to its west, and has the town of Llanfairfechan towards the north.

When the list of Welsh 500m P15s that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with 40m of drop, based on the 536m summit spot height and the 496m bwlch spot height that appear on the Ordnance Survey 1:25,000 Explorer map.

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

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

LIDAR summit image of Foel Ganol (SH 687 715)

LIDAR analysis gives the summit of this hill as 533.1m positioned at SH 68797 71588, and when compared to its originally listed summit height of 536m 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 533.1m and this was derived from LIDAR analysis, this is 2.9m lower than the originally listed summit height of 536m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Carnedd Llywelyn

Name: Foel Ganol

OS 1:50,000 map: 115

Summit Height (New Height): 533.1m (LIDAR)

Summit Grid Reference: SH 68797 71588 (LIDAR)

Bwlch Height: 495.0m (LIDAR)

Bwlch Grid Reference: SH 69012 71563 (LIDAR)

Drop: 38.2m (LIDAR)

Myrddyn Phillips and Aled Williams (September 2024)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Pt. 631.7m (SH 733 622) - 34th significant height revision

There has been a Significant Height Revision to a hill that is listed in the 600m Twmpau and the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams.

Pt. 631.7m (SH 733 622)

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

600m Twmpau - Welsh hills at or above 600m and below 700m in height with 30m minimum drop, with an accompanying sub list entitled the 600m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 600m and below 700m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips and is available to download in Google Doc format from Mapping Mountains.

600m Twmpau by Myrddyn Phillips

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The hill is being listed by the point (Pt. 631.7m) notation and it is adjoined to the Carnedd Llywelyn 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 A5 road to its south-west and the B5106 and A470 roads to its east, and has the village of Capel Curig towards the south south-west.

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

When the original list that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 36m of drop based on the 634m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 598m bwlch height based on interpolation of 10m contouring between 590m – 600m. The drop value for this hill was later amended to 36m, based on the 598m 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.

LIDAR image of Pt. 631.7m (SH 733 622)

LIDAR summit image of Pt. 631.7m (SH 733 622)

The summit height produced by LIDAR analysis is 631.7m and is positioned at SH 73366 62247 and SH 73365 62246, 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 631.7m and this was derived from LIDAR analysis, this is 2.3m lower than the previously listed summit height of 634m, which was based on the 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: Carnedd Llywelyn

Name: Pt. 631.7m

OS 1:50,000 map: 115

Summit Height (New Height): 631.7m (LIDAR)

Summit Grid Reference: SH 73366 62247 & SH 73365 62246 (LIDAR)

Bwlch Height: 595.9m (LIDAR)

Bwlch Grid Reference: SH 73256 62104 (LIDAR)

Drop: 35.8m (LIDAR)

Myrddyn Phillips and Aled Williams (September 2024)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Foel Fras (SH 696 681) - 33rd significant height revision

Summit Relocations post for Foel Fras

There has been a Significant Height Revision to a hill that is listed in the Y Pellennig – The Remotest Hills of Wales, Welsh Highlands – Uchafion Cymru and 900m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Leica RX1250 survey conducted by Alan Dawson.

Foel Fras (SH 696 681) from the summit of Trwsgl (SH 663 679)

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

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

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

900m Twmpau - Welsh hills at or above 900m and below 1000m in height with 30m minimum drop, with an accompanying sub list entitled the 900m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 900m and below 1000m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips and is available to download in Google Doc format from Mapping Mountains.

900m Twmpau by Myrddyn Phillips

The name the hill is listed by is Foel Fras and it is adjoined to the Carnedd Llywelyn 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 to its north-west, the A5 road to its south-west and the B5106 and A470 roads to its east, and has the town of Bethesda towards the west south-west.

When the original list that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with 58m of drop, based on the 942m summit spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and the 884m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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

However, the summit area of this hill is rocky and includes a number of substantial upright rock spikes. One of the earliest Abney Level surveys to ascertain the high point of this hill was conducted in 2011 by Graham Jackson. This survey concluded that a rock spike approximately 55 metres south-wesward of the trig pillar is the highest point of this hill.

This rock spike was subsequently surveyed by Alan Dawson using the Leica RX1250, resulting in a 944.1m summit height positioned at SH 69611 68118, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The Leica RX1250 gathering data at the summit of Foel Fras (SH 696 681). Photo: Alan Dawson

Therefore, the new listed summit height of this hill is 944.1m and this was derived from a Leica RX1250 survey, this is 2.1m higher than the previously listed height of 942m, which was based on the spot height adjoined to a trinagulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group: Carnedd Llywelyn

Name: Foel Fras

OS 1:50,000 map: 115

Summit Height (New Height): 944.1m (converted to OSGM15, Leica RX1250)

Summit Grid Reference: SH 69611 68118 (Leica RX1250)

Bwlch Height: 881.3m (converted to OSGM15, Leica RX1250)

Bwlch Grid Reference: SH 68799 66515 (Leica RX1250)

Drop: 62.8m (Leica RX1250)

Remoteness: 3.975km

Myrddyn Phillips and Aled Williams (August 2024)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Tryfan (SH 596 580) - 32nd significant height revision

Survey post for Tryfan

Tryfan (SH 596 580)

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

500m Twmpau by Myrddyn Phillips

Welsh Highlnads - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The name the hill is listed by is Tryfan and it is adjoined to the Yr Wyddfa 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 A4086 road to its north-east, and has the village of Llanberis towards the north-west.

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

A basic levelling survey conducted by Myrddyn Phillips on the 25.06.04 gave this hill 67ft (20.4m) of drop and therefore it was included in the listing that later became known as the Welsh Highlands – Uchafion Cymru. However, this drop value was at odds with detail on the contemporary Ordnance Survey 1:25,000 Explorer map which has an uppermost 560m summit contour and bwlch contouring between 550m – 560m, with interpolation giving an estimated c 555m bwlch height.

Extract from the interactive mapping hosted on the WalkLakes website

The drop value ascertained fron the basic levelling survey implied that current Ordnance Survey contouring on the 1:50,000 Landranger and 1:25,000 Explorer map is missing an uppermost 570m ring contour, and this is evidenced by the 577m summit spot height on the mapping hosted on the WalkLakes website. This website hosts an interactive map originated from the Ordnance Survey Open Data programme and has many spot heights not on other publicly available maps.

The Trimble GeoXH 6000 gathering data at the summit of Tryfan (SH 596 580)

The summit of this hill was subsequently surveyed with the Trimble GeoXH 6000 on the 09.09.14, resulting in a 577.2m summit height positioned at SH 59636 58098, and this height 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 577.2m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SH 59636 58098 and is 17.2m higher than the uppermost 560m contour 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: Yr Wyddfa

Name: Tryfan

OS 1:50,000 map: 115

Summit Height (New Height): 577.2m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference: SH 59636 58098 (Trimble GeoXH 6000)

Bwlch Height: 556.4m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference: SH 59683 57996 (Trimble GeoXH 6000)

Drop: 20.8m (Trimble GeoXH 6000)

Myrddyn Phillips and Aled Williams (August 2024)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Tryfan (SH 597 578) - 31st significant height revision

Survey post for Tryfan

Tryfan (SH 597 578)

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

500m Twmpau by Myrddyn Phillips

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

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

A basic levelling survey conducted by Myrddyn Phillips on the 25.06.04 gave this hill 79½ft (24.2m) of drop and therefore it was included in the listing that later became known as the Welsh Highlands – Uchafion Cymru. However, this drop value was at odds with detail on the contemporary Ordnance Survey 1:25,000 Explorer map which has an uppermost 580m summit contour and bwlch contouring between 560m – 570m, with interpolation giving an estimated c 568m bwlch height.

Extract from the interactive mapping hosted on the WalkLakes website

The drop value ascertained fron the basic levelling survey implied that current Ordnance Survey contouring on the 1:50,000 Landranger and 1:25,000 Explorer map is missing an uppermost 590m ring contour, and this is evidenced by the 594m summit spot height on the mapping hosted on the WalkLakes website. This website hosts an interactive map originated from the Ordnance Survey Open Data programme and has many spot heights not on other publicly available maps.

The Trimble GeoXH 6000 gathering data at the summit of Tryfan (SH 597 578)

The summit of this hill was subsequently surveyed with the Trimble GeoXH 6000 on the 09.09.14, resulting in a 594.4m summit height positioned at SH 59763 57873, and this height 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 594.4m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SH 59763 57873 and is 14.4m higher than the uppermost 590m contour 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: Yr Wyddfa

Name: Tryfan

OS 1:50,000 map: 115

Summit Height (New Height): 594.4m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference: SH 59763 57873 (Trimble GeoXH 6000)

Bwlch Height: 569.9m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference: SH 59858 57775 (Trimble GeoXH 6000)

Drop: 24.6m (Trimble GeoXH 6000)

Myrddyn Phillips and Aled Williams (August 2024)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Y Foel Goch (SH 677 582) - 30th significant height revision

There has been a Significant Height Revision to a hill that is listed in the Welsh Highlands – Uchafion Cymru and 800m Twmpau, 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 Y Foel Goch (SH 677 582)

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

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

800m Twmpau - Welsh hills at or above 800m and below 900m in height that have 30m minimum drop, with an accompanying sub list entitled the 800m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 800m and below 900m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips and the details to it were published on Mapping Mountains on the 15^th March 2015.

800m Twmpau by Myrddyn Phillips

The name the hill is listed by is Y Foel Goch and it is adjoined to the Glyder Fawr 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 A5 road to its north and the A4086 road to its south, and has the village of Capel Curig towards the east.

Prior to LIDAR analysis this hill was listed with 63m of drop, based on the 805m summit spot height and the 742m bwlch spot height that appear on the contemporary Ordnance Survey 1:25,000 Explorer map.

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

LIDAR summit image of Y Foel Goch (SH 677 582)

The summit height produced by LIDAR analysis is 807.2m and is positioned at SH 67783 58216, 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 807.2m and this was derived from LIDAR analysis, this is 2.2m higher than the previously listed summit height of 805m, which was based on the 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: Glyder Fawr

Name: Y Foel Goch

OS 1:50,000 map: 115

Summit Height (New Height): 807.2m (LIDAR)

Summit Grid Reference: SH 67783 58216 (LIDAR)

Bwlch Height: 742.5m (LIDAR)

Bwlch Grid Reference: SH 67252 58277 (LIDAR)

Drop: 64.8m (LIDAR)

Myrddyn Phillips and Aled Williams (July 2024)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Pt. 505.8m (SN 785 598) - 29th significant height revision

Survey post for Pt. 505.8m

Hill Reclassifications post for Pt. 505.8m

There has been a Significant Height Revision to a hill that is listed in the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams.

LIDAR image of Pt. 505.8m (SN 785 598)

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

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The hill is being listed by the point (Pt. 505.8m) notation 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-west and south, and has the small community of Pontrhydfendigaid towards the north-west and the town of Tregaron towards the west.

Extract from the Ordnance Survey series of Six-Inch maps

When the initial P10 sub list was completed in June 2020 this hill was listed with an estimated c 9m of drop, based on the 1649ft (502.6m) height that appeared on the Ordnance Survey series of Six-Inch maps and an estimated c 494m bwlch height, based on interpolation of 5m contouring that appeared on online mapping.

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

The height that appeared on the Ordnance Survey series of Six-Inch maps was at odds with the 506m spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 78576 59903, however this spot height was not supported by contemporary contour information on large scaled Ordnance Survey maps.

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

LIDAR summit image of Pt. 505.8m (SN 785 598)

LIDAR analysis gives the highest ground on this hill as 505.8m positioned at SN 78575 59899, 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 505.8m and this was derived from LIDAR analysis, this is 3.2m higher than the previously listed summit height which was derived from the 1649ft (502.6m) height that appeared on the Ordnance Survey series of Six-Inch maps.

The full details for the hill are:

Group: Esgair Wen

Name: Pt. 505.8m

OS 1:50,000 map: 146, 147

Summit Height (New Height): 505.8m (LIDAR)

Summit Grid Reference: SN 78575 59899 (LIDAR)

Bwlch Height: 492.4m (LIDAR)

Bwlch Grid Reference: SN 78513 60070 (LIDAR)

Drop: 13.5m (LIDAR)

Myrddyn Phillips and Aled Williams (November 2023)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Clo Cadno (SO 118 162) - 28th significant height revision

Hill Reclassifications post for Clo Cadno

Survey post for Clo Cadno

Clo Cadno (SO 118 162)

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

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Clo Cadno and it is adjoined to the Cefn yr Ystrad group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and is positioned with minor roads to its north-west and south-west and the B4560 road to its east, and has the village of Llangynidr towards the north-east and the small community of Trefil towards the south.

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

When the list that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was not included as the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map have an uppermost 520m ring contour with bwlch contouring between 510m – 520m.

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

The details for this hill were re-examined via mapping on the OS Maps website. This is the replacement for OS Get-a-map and had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, and this mapping indicated that this hill had a minimum of 15m of drop.

Extract from the interactive mapping that was hosted on the OS Maps website

LIDAR image of Clo Cadno (SN 118 162)

LIDAR analysis gives the highest ground on this hill as 530.3m positioned at SO 11849 16247, 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 530.3m and this was derived from LIDAR analysis, this is 10.3m higher than the uppermost 520m ring contour 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: Cefn yr Ystrad

Name: Clo Cadno

OS 1:50,000 map: 161

Summit Height (New Height): 530.3m (LIDAR)

Summit Grid Reference: SO 11849 16247 (LIDAR)

Bwlch Height: 513.6m (LIDAR)

Bwlch Grid Reference: SO 12197 15992 (LIDAR)

Drop: 16.7m (LIDAR)

Myrddyn Phillips and Aled Williams (October 2023)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Pt. 510.0m (SH 819 314) - 27th significant height revision

Hill Reclassifications post for Pt. 510.0m

LIDAR image of Pt. 510.0m (SH 819 314)

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

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The hill is being listed by the point (Pt. 510.0m) notation and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor road to its north-east and the A494 road to its south-east, and has the town of Y Bala towards the east north-east.

When the initial P10 sub list was completed in June 2020 this hill was listed with 9m of drop, based on the 508m summit spot height which appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the 499.0m bwlch height ascertained from 1m DSM LIDAR analysis.

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

However, it was not until full LIDAR coverage 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 analysis gives the highest ground on this hill as 510.0m positioned at SH 81962 31463, 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 510.0m and this was derived from LIDAR analysis, this is 2.0m higher than the previously listed height of 508m which was based on the 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: Arenig Fawr

Name: Pt. 510.0m

OS 1:50,000 map: 124, 125

Summit Height (New Height): 510.0m (LIDAR)

Summit Grid Reference: SH 81962 31463 (LIDAR)

Bwlch Height: 499.1m (LIDAR)

Bwlch Grid Reference: SH 82130 31691 (LIDAR)

Drop: 10.9m (LIDAR)

Myrddyn Phillips and Aled Williams (September 2023)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Pt. 714.3m (SH 627 359) - 26th significant height revision

There has been a Significant Height Revision to a hill that is listed in the Y Pellennig – The Remotest Hills of Wales, Welsh Highlands – Uchafion Cymru and 700m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams.

LIDAR image of Pt. 714.3m (SH 627 359)

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

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

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

700m Twmpau - Welsh hills at or above 700m and below 800m in height with 30m minimum drop, with an accompanying sub list entitled the 700m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 700m and below 800m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips and is available to download in Google Doc format from Mapping Mountains.

The 700m Twmpau by Myrddyn Phillips

The hill is being listed by the point (Pt. 714.3m) notation and it is adjoined to the Arenig Fawr group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and it is positioned with a minor roads to the north, south-west and east, and the A4212 road farther to its north, and has the town of Y Bala towards the east.

When the original list that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with 18m of drop, based on an eye and spirit level survey conducted by John and Anne Nuttall that resulted in 60ft (18.3m) of drop, and it was originally listed with a 712m summit height based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and a 694m bwlch height.

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

LIDAR summit image of Pt. 714.3m (SH 627 359)

Therefore, the new listed summit height of this hill is 714.3m and this was derived from LIDAR analysis, this is 2.3m higher than the previously listed height of 712m which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group: Arenig Fawr

Name: Pt. 714.3m

OS 1:50,000 map: 124, 125

Summit Height (New Height): 714.3m (LIDAR)

Summit Grid Reference: SH 82741 35938 (LIDAR)

Bwlch Height: 693.6m (LIDAR)

Bwlch Grid Reference: SH 82725 36128 (LIDAR)

Drop: 20.7m (LIDAR)

Remoteness: 2.925km

Myrddyn Phillips and Aled Williams (August 2023)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Llechwedd Du (SH 893 446) - 25th significant height revision

Hill Reclassifications post for Llechwedd Du

LIDAR image of Llechwedd Du (SH 893 446)

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

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Llechwedd Du and it is adjoined to the Carnedd y Filiast group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A2), and is positioned with the A4212 road to its south and the B4501 road to its east, and has the town of Y Bala towards the south south-east and the village of Cerrigydrudion towards the north-east.

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

When the original list that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was included as a Welsh Highland Sub with 14m of drop, based on the 509m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the 495m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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

The details for this hill were re-assessed when the OS Maps website became available online. This is the replacement for OS Get-a-map and had contours at 5m intervals which were consistently more accurate compared to the 5m contours that sometimes appeared on Ordnance Survey 1:25,000 Explorer maps and the online Vector Map Local. This re-assessment resulted in its reclassification to Welsh Highland P15 status and listed with an estimated c 16m of drop, based on an estimated c 511m summit height from interpolation of the 510m uppermost contour and the 495m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

Extract from the interactive mapping hosted on the OS Maps website

LIDAR analysis gives the highest ground on this hill as 511.4m positioned at SH 89360 44629, 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 511.4m and this was derived from LIDAR analysis, this is positioned at SH 89360 44629 and is 2.4m higher than its originally listed height of 509m, which was based on the summit 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: Carnedd y Filiast

Name: Llechwedd Du

OS 1:50,000 map: 124, 125

Summit Height (New Height): 511.4m (LIDAR)

Summit Grid Reference: SH 89360 44629 (LIDAR)

Bwlch Height: 497.1m (LIDAR)

Bwlch Grid Reference: SH 89096 44273 (LIDAR)

Drop: 14.3m (LIDAR)

Myrddyn Phillips and Aled Williams (May 2023)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Castell y Gwynt (SH 653 581) - 24th significant height revision

1st Survey post for Castell y Gwynt

2nd Survey post for Castell y Gwynt

Castell y Gwynt (SH 653 581)

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

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Castell y Gwynt and it is adjoined to the Glyder Fawr 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 A5 road to its north and the A4086 road to its south, and has the village of Capel Curig towards the east.

When the list that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with 16m of drop, based on a series of basic levelling surveys conducted by Myrddyn Phillips and listed with a 972m summit height, based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map and a 956m bwlch height, based on the height difference between the summit spot height and the drop value ascertained from the basic levelling survey.

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

The summit of this hill has now been surveyed twice with the Trimble GeoXH 6000 and it is the average of these results that is being taken, resulting in a 975.7m summit height positioned at SH 65397 58181, and this height 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 Castell y Gwynt on the 16.05.14

Therefore, the new listed summit height of this hill is 975.7m and this was derived from the average of two Trimble GeoXH 6000 surveys, this is positioned at SH 65397 58181 and is 3.7m higher than its previously listed height of 972m which was based on the summit spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group: Glyder Fawr

Name: Castell y Gwynt

OS 1:50,000 map: 115

Summit Height (New Height): 975.7m (converted to OSGM15)

Summit Grid Reference: SH 65397 58181

Bwlch Height: 959.7m (converted to OSGM15)

Bwlch Grid Reference: SH 65419 58194

Drop: 16.0m

Myrddyn Phillips and Aled Williams (May 2023)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Craig Eigiau (SH 712 646) - 23rd significant height revision

Survey Post for Craig Eigiau

Hill Reclassifications post for Craig Eigiau

Craig Eigiau (SH 712 646) (Photo: Aled Williams)

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

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Craig Eigiau and it is adjoined to the Carnedd Llywelyn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with a minor road to its north-east, the A5 road to its south-west and the B5106 road and the A470 road to its east, and has the town of Llanrwst towards the east south-east.

The contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map do not show any meaning contours for this hill that imply its true height, as each only has an uppermost 670m contour.

Extract from the Ordnance Survey 1:25,00 Explorer map

LIDAR analysis gives this hill 9.7m of drop, based on a 688.1m summit height and a 678.4m bwlch height. This hill has now been surveyed with the Trimble GeoXH 6000, resulting in a 688.4m summit height positioned at SH 71280 64670 and 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:

The Trimble GeoXH 6000 gathering data at the summit of Craig Eigiau (SH 712 646) (Photo: Aled Williams)

Therefore, the new listed summit height of this hill is 688.4m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SH 71280 64670 and is 18.4m higher than the uppermost 670m contour on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group: Carnedd Llywelyn

Name: Craig Eigiau

OS 1:50,000 map: 115

Summit Height (New Height): 688.4m (converted to OSGM15)

Summit Grid Reference: SH 71280 64670

Bwlch Height: 678.2m (converted to OSGM15)

Bwlch Grid Reference: SH 71218 64674

Drop: 10.2m

Aled Williams and Myrddyn Phillips (April 2023)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Blorens (SO 269 118) - 22nd significant name change

Survey post for Blorens

Blorens (SO 269 118)

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

The 500m Twmpau by Myrddyn Phillips

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Blorens and it is adjoined to the Cefn yr Ystrad group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A465 road to its north-east, the B4246 road to its north-west and a minor road to its south, and has the town of Y Fenni (Abergavenny) towards the north-east.

When the list of Welsh 500m P15s that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 133m of drop, based on the 561m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 428m bwlch height, based on interpolation of 10m contouring between 420m – 430m.

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

The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in a 558.9m summit height positioned at SO 26974 11830, and this height 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 Blorens

Therefore, the new listed summit height of this hill is 558.9m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SO 26974 11830 and is 2.1m lower than its originally listed height of 561m, which was based on the summit 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: Cefn yr Ystrad

Name: Blorens

OS 1:50,000 map: 161

Summit Height (New Height): 558.9m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference: SO 26974 11830 (Trimble GeoXH 6000)

Bwlch Height: 426.9m (LIDAR)

Bwlch Grid Reference: SO 21949 10939 (LIDAR)

Drop: 132.0m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Aled Williams and Myrddyn Phillips (March 2023)

Mapping Mountains - Significant Height Revisions - Welsh Highlands - Uchafion Cymru

Tryfan (SH 664 594) - 21st significant height revision

Survey post for Tryfan

Tryfan (SH 664 594) (Photo: Aled Williams)

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

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Tryfan and it is adjoined to the Glyder Fawr 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 A5 road to its north and the A4086 road to its south, and has the village of Capel Curig towards the east south-east.

When the P10 sub list was compiled this hill was listed with 12.6m of drop, based on a basic levelling survey conducted by Myrddyn Phillips on the 01.05.98, with the summit height listed as 899m and the bwlch height as 886m, with both heights based on interpolation of contouring that appear on contemporary Ordnance Survey maps.

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

The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in a 900.0m summit height positioned at SH 66422 59485, and this height comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The Trimble set-up position at the summit of Tryfan (SH 664 594) (Photo: Aled Williams)

The Trimble GeoXH 6000 gathering data at the summit of Tryfan (SH 664 594) (Photo: Aled Williams)

Therefore, the new listed summit height of this hill is 900.0m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SH 66422 59485 and is 1.0m higher than its previously listed height of 899m which was based on the drop value ascertained from a basic levelling survey compared to Ordnance Survey map contouring, and is 10.0m higher than the uppermost contour on the contemporary Ordnance Survey 1:25000 Explorer map.

The full details for the hill are:

Group: Glyder Fawr

Name: Tryfan

OS 1:50,000 map: 115

Summit Height (New Height): 900.0m (converted to OSGM15)

Summit Grid Reference: SH 66422 59485

Bwlch Height: 887.5m (converted to OSGM15)

Bwlch Grid Reference: SH 66385 59441

Drop: 12.5m

Aled Williams and Myrddyn Phillips (March 2023)

On 7^th January 2023 the Sub hills accompanying the main listing of the Welsh Highlands – Uchafion Cymru were amended. The 490m Subs and 490m Double Subs have been dispensed with, and the remaining 500m Subs are now entitled the Welsh Highland Subs and their criteria amended to include all Welsh hills at and above 500m in height with 10m or more and below 15m of drop.

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Great Creigiau (SO 198 636) - 20th significant height revision

Survey post for Great Creigiau

There has been a Significant Height Revision to a hill that was considered for inclusion in the list of The Welsh Highlands – Uchafion Cymru, 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.

Great Creigiau (SO 198 636)

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

The Welsh Highlands – Uchafion Cymru – This is the revised draft title for the Welsh 500m P15s list that takes in all hills in Wales at or above 500m in height with 15m minimum drop. Accompanying the main list are three sub lists, these are; 500m Sub-Uchaf, 490m Sub-Uchaf and the Double Sub category, with this hill being considered for 500m Sub-Uchaf satus. The criteria for which are all Welsh hills at or above 500m in height with 14m or more and below 15m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams with the Introduction to the list being published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19^th June 2019.

The Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Great Creigiau and it is adjoined to the Fforest Glud group of hills, which are situated in the eastern part of Mid and West Wales (Region B, Sub-Region B1), and it is positioned with the A488 road to its north, the A44 road to its south and the B4372 road to its south-east, and has the village of Maesyfed (New Radnor) towards the south south-east.

This hill was not included as a P14 Sub in the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru, as with a 646m summit spot height and bwlch contouring between 630m – 640m that appear on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, this contouring implied that the hill did not have sufficient drop to be considered for P14 500m Sub-Uchaf status.

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

The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in 643.4m positioned at SO 19810 63643 and this height 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 Great Creigiau

Therefore, this hill’s new listed summit height is 643.4m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SO 19810 63643 and is 2.6m lower than its previously listed height of 646m which appears as a spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Group: Fforest Glud

Name: Great Creigiau

OS 1:50,000 map: 148

Summit Height (New Height): 643.4m (converted to OSGM15)

Summit Grid Reference: SO 19810 63643

Bwlch Height: 633.3m (converted to OSGM15)

Bwlch Grid Reference: SO 19959 63879

Drop: 10.1m

Myrddyn Phillips and Aled Williams (August 2021)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Twyn Crug yr Afan (SS 920 954) - 19th significant height revision

Survey post for Twyn Crug yr Afan

There has been a Significant Height Revision to a hill that is listed in the 500m Twmpau and The Welsh Highlands – Uchafion Cymru, 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.

Twyn Crug yr Afan (SS 920 954)

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

The 500m Twmpau by Myrddyn Phillips

The Welsh Highlands – Uchafion Cymru – This is the revised draft title for the Welsh 500m P15s list that takes in all hills in Wales at or above 500m in height with 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams with the introduction to the list being published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19^th June 2019.

The Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Twyn Crug yr Afan and it is adjoined to the Cymoedd Morgannwg group of hills, which are situated in the central part of South Wales (Region C, Sub-Region C2), and it is positioned with the A4058 road to its north-east and the A4107 road to its immediate south, and has the connecting villages of Blaengwynfi and Abergwynfi towards the west north-west.

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

When the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with 31m of drop, based on the 558m spot height that appears on the Ordnance Survey 1:50,000 Landranger map and the 527m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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

Since the original compilation of this list there have been a number of Ordnance Survey maps made available online, some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website, whilst others are current and digitally updated such as the old Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and the mapping on the OS Maps, Magic Maps and WalkLakes websites.

The details for this hill were reassessed 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 maps and for this hill it had a 559m summit spot height adjoined to the ancient tumulus and positioned at SS 92037 95445.

One of the mapping resources now available online is the Magic Maps website which hosts an interactive map originated from Ordnance Survey data. This mapping also has many spot heights not on other publicly available Ordnance Survey maps and for this hill the 559m summit spot height is also shown.

Extract from the Magic Maps website

The summit of this hill has now been surveyed with the Trimble GeoXH 6000, resulting in 560.2m positioned at SS 92035 95448 and this height 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 Twyn Crug yr Afan

Therefore, this hill’s new listed summit height is 560.2m and this was derived from a Trimble GeoXH 6000 survey, this is positioned at SS 92035 95448 and is 2.2m higher than its originally listed height of 558m which appears as a spot height on contemporary Ordnance Survey 1:50,000 Landranger maps, and 1.2m higher than the 559m 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 which now appears on the interactive mapping on the Magic Maps website.

The full details for the hill are:

Group: Cymoedd Morgannwg

Name: Twyn Crug yr Afan

OS 1:50,000 map: 170

Summit Height (New Height): 560.2m (converted to OSGM15)

Summit Grid Reference: SS 92035 95448

Bwlch Height: 526.0m (converted to OSGM15)

Bwlch Grid Reference: SS 92019 95054

Drop: 34.2m

Aled Williams and Myrddyn Phillips (August 2021)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Cefn Dylif (SJ 089 369) - 18th significant height revision

Survey post for Cefn Dylif

There has been a Significant Height Revision to a hill that is listed in the 600m Twmpau, The Welsh Highlands – Uchafion Cymru and Y Pellennig – The Remotest 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 with assistance from Mark Trengove.

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

The 600m Twmpau by Myrddyn Phillips

The Welsh Highlands – Uchafion Cymru – This is the revised draft title for the Welsh 500m P15s list that takes in all hills in Wales at or above 500m in height with 15m minimum drop. Accompanying the main list are three sub lists, these are; 500m Sub-Uchaf, 490m Sub-Uchaf and the Double Sub category. The list is co-authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19^th June 2019.

The Welsh Highlands - Uchafion Cymru by Myrddyn Phillipa and Aled Williams

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

The name the hill is listed by is Cefn Dylif 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 positioned with the A5 road to its north, the B4401 road to its west and the B4391 road to its south-west, and has the village of Llandrillo towards the west.

When the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 36m of drop based on the 621m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 585m bwlch height based on interpolation of 10m contouring between 580m – 590m. The drop value for this hill was later amended to an estimated c 38m, based on an estimated c 583m bwlch height based on interpolation of 5m contouring between 580m – 585m that appeared on the OS Maps website.

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

The summit of this hill was now been surveyed with the Trimble GeoXH 6000, resulting in a height of 618.3m. This is not a dramatic height revision when compared to some survey results, 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 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 Cefn Dylif

Therefore, this hill’s new listed summit height is 618.3m and this was derived from a Trimble GeoXH 6000 survey, this is 2.7m lower than the previously listed height of 621m which was based on the spot height that appears on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group: Y Berwyn

Name: Cefn Dylif

OS 1:50,000 map: 125

Summit Height (New Height): 618.3m (converted to OSGM15)

Summit Grid Reference: SJ 08943 36942

Bwlch Height: 581.3m (converted to OSGM15)

Bwlch Grid Reference: SJ 09068 36590

Drop: 37.0m

Myrddyn Phillips and Aled Williams (June 2021)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Carreg Croes Ifor (SO 248 106) - 17th significant height revision

Summit Relocations post for Carreg Croes Ifor

There has been a Significant Height Revision to a hill that is listed in the 500m Twmpau and The Welsh Highlands – Uchafion Cymru, 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 summit survey conducted by Aled Williams.

LIDAR image of Carreg Croes Ifor (SO 248 106)

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

The Welsh Highlands – Uchafion Cymru – This is the revised draft title for the Welsh 500m P15s list that takes in all hills in Wales at or above 500m in height with 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams with the Introduction to the list being published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19th June 2019.

The name the hill is listed by is Carreg Croes Ifor and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is positioned with the A465 road to its north, the B4248 road to its south-west and the B4246 road to its east, and has the town of Blaenafon towards the south south-east.

When the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 18m of drop based on a non-interpolated c 500m summit height and a 482m bwlch height taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

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

Since first compilation of the Welsh 500m P15 list there are a number of maps now available online, and the details for this hill were re-assessed when the Ordnance Survey 1:25,000 Historical map became available online, and this map gives a 1657ft (505.1m) summit spot height for this hill.

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

The imperial height on the Ordnance Survey 1:25,000 Historical map is derived from a 1657.4m (505.2m) Surface Height that appears on the Ordnance Survey series of Six-Inch maps. Therefore, the summit height for this hill was revised and listed as 505m with the caveat that since this height was derived this hill has undergone mining activity which has substantially altered the landscape.

Extract from the Ordnance Survey series of Six-Inch maps

LIDAR summit image for Carreg Croes Ifor

The summit height and position produced by LIDAR analysis is 509.8m at SO 24848 10663, this is a dramatic height revision when compared to some revised heights, and it comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

During analysis of this hill, Aled used overlays from old maps with contemporary maps and the details produced via LIDAR. This shows that the natural 505.2m summit positioned at SO 24810 10620 is now under a substantial amount of mine spoil and this has raised the height of the summit.

The summit of this hill has now been surveyed with the Trimble GeoXH 6000 and as the natural summit is now under a spoil tip and an on-site visit confirms this artificially raised summit to be solid and stable, it is the Trimble summit height and position that is being prioritised for this hill.

Therefore, the new listed summit height of this hill is 509.7m and this was derived from a Trimble GeoXH 6000 survey, this is 4.7m higher than the 505m summit height that was previously given for this hill.

The full details for the hill are:

Group: Cymoedd Gwent

Name: Carreg Croes Ifor

OS 1:50,000 map: 161

Summit Height (New Height): 509.7m (converted to OSGM15, Trimble GeoXH 6000, artificially raised)

Summit Grid Reference: SO 24848 10663 (Trimble GeoXH 6000)

Bwlch Height: 482.1m (LIDAR)

Bwlch Grid Reference: SO 25485 10565 (LIDAR)

Drop: 27.6m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Aled Williams and Myrddyn Phillips (May 2020)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Carnedd y Filiast (SH 620 627) - 16th significant height revision

Survey post for Carnedd y Filiast

There has been a Significant Height Revision to a hill that appears in the listings of Yr Uchafion and 800m Twmpau, 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 and Aled Williams which took place on the 6^th July 2019.

Carnedd y Filast (SH 620 627)

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

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to the list appearing on Mapping Mountains on the 4^th November 2015 and an update relating to the list appearing on Mapping Mountains on the 19^th June 2019.

800m Twmpau - Welsh hills at or above 800m and below 900m in height with 30m minimum drop, with an accompanying sub list entitled the 800m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 800m and below 900m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips and the details to it were published on Mapping Mountains on the 15^th March 2015.

The name of the hill is Carnedd y Filiast and it is adjoined to the Glyderau 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 Afon Ogwen and the A5 road to its north-east and Llyn Padarn, Llyn Peris and the A4086 road towards its south-west, and has the town of Bethesda towards the north and the village of Llanberis towards the west south-west.

Prior to the Trimble GeoXH 6000 survey the height of the hill was listed as 821m which is based on the summit 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

The summit height produced by the Trimble GeoXH 6000 is 823.6m, this is not a dramatic height revision when compared to some survey results, 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 Carnedd y Filiast

Therefore, this hill’s new summit height as surveyed with the Trimble GeoXH 6000 is 823.6m, this is positioned at SH 62040 62733 and is 2.6m higher than its previously listed height of 821m which appears as a spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group: Glyderau

Name: Carnedd y Filiast

OS 1:50,000 map: 115

Summit Height (New Height): 823.6m (converted to OSGM15)

Summit Grid Reference: SH 62040 62733

Bwlch Height: 744.4m (converted to OSGM15)

Bwlch Grid Reference: SH 61995 61535

Drop: 79.1m

For details on the survey of this hill

Myrddyn Phillips and Aled Williams (October 2019)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Pt. 690.2m (SH 647 468) - 15th significant height revision

Survey post for Pt. 690.2m

There has been a Significant Height Revision to a hill that is listed in the Yr Uchafion, 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 on the 23^rd March 2019.

Pt. 690.2m (SH 647 468)

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

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to this list appearing on Mapping Mountains on the 4^th November 2015.

The hill is currently listed by the point (Pt. 690.2m) notation and it is adjoined to the Moelwynion range of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A4085 road to its south-west, the A498 road to its north-west and the A470 road towards the east, and has the small community of Croesor towards the south-west and the town of Blaenau Ffestiniog towards the east.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with a 688m summit height which appears as a spot height on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map.

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

The summit height produced by the Trimble GeoXH 6000 survey is 690.2m, this is not a substantial height revision when compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

The Trimble GeoXH 6000 gathering data at the summit of Pt. 690.2m (SH 647 468)

Therefore, the new summit height of this hill is 690.2m and this was produced by surveying with the Trimble GeoXH 6000, this is 2.2m higher than its previously listed height of 688m which appears as a spot height on the Ordnance Survey Vector Map Local hosted on the Geograph website, however this new height is in accordance with the 5m contouring on OS Maps.

Extract from the OS Maps website

The full details for the hill are:

Group: Moelwynion

Name: Pt. 690.2m

OS 1:50,000 map: 115

Summit Height (New height): 690.2m (converted to OSGM15)

Summit Grid Reference: SH 64799 46864

Bwlch Height: 670.9m (converted to OSGM15)

Bwlch Grid Reference: SH 64681 46742

Drop: 19.3m

For details on the survey of this hill

Myrddyn Phillips and Aled Williams (July 2019)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Cnicht (SH 645 466) - 14th significant height revision

Survey post for Cnicht

There has been a Significant Height Revision to a hill that is listed in the 600m Twmpau and Yr Uchafion, 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 on the 23^rd March 2019.

Cnicht (SH 645 466)

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

600m Twmpau – Welsh hills at or above 600m and below 700m in height that have 30m minimum drop, with an accompanying sub category entitled the 600m Sub-Twmpau consisting of all Welsh hills at or above 600m and below 700m in height that have 20m or more and below 30m of drop. With the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips.

The name of the hill is Cnicht, and it is adjoined to the Moelwynion range of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A4085 road to its south-west, the A498 road to its north-west and the A470 road towards the east, and has the small community of Croesor towards the south-west and the town of Blaenau Ffestiniog towards the east.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with a 689m summit height that appears as a spot height on the Ordnance Survey 1:50,000 Landranger and 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 690.7m, this is not a substantial 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 Cnicht

Therefore, this hill’s new summit height is 690.7m and this was produced by surveying with the Trimble GeoXH 6000, this is 1.7m higher than its previously listed height of 689m which appears as a spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, however this new height is in accordance with the 5m contouring on OS Maps.

Extract from the OS Maps website

The full details for the hill are:

Group: Moelwynion

Name: Cnicht

OS 1:50,000 map: 115

Summit Height (New height): 690.7m (converted to OSGM15)

Summit Grid Reference: SH 64545 46613

Bwlch Height: 585.7m (converted to OSGM15)

Bwlch Grid Reference: SH 65589 47707

Drop: 105.0m

For details on the survey of this hill

Myrddyn Phillips and Aled Williams (July 2019)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Foel Lwyd (SH 720 723) - 13th significant height revision

Survey post for Foel Lwyd

There has been a Significant Height Revision to a hill that is listed in the Yr Uchafion and 600m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Leica GS15 summit survey conducted by John Barnard, Graham Jackson and Myrddyn Phillips and LIDAR bwlch analysis conducted by Aled Williams.

Foel Lwyd (SH 720 723)

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

The name the hill is listed as is Foel Lwyd, and it is adjoined to the Carneddau range of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the A 55 road to its north and the Afon Conwy and the A 470 road to its east, and has the town of Penmaenmawr towards the north.

Prior to the survey with the Leica GS15 this hill was listed with an estimated c 54m of drop, based on the 603m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map, and an estimated c 549m bwlch height based on interpolation of 10m contouring between 540m - 550m.

Extract from the Ordnance Survey Vector Map local hosted on the Geograph website and which is entitled the Interactive Coverage Map

The summit height produced by the Leica GS15 survey is 600.2m, this is not a substantial 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 Leica GS15 set-up position at the summit of Foel Lwyd

Therefore, this new listed summit height of this hill is 600.2m and this was derived by a Leica GS15 survey, this is 2.8m lower than its previously listed height of 603m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map.

The full details for the hill are:

Group: Carneddau

Name: Foel Lwyd

OS 1:50,000 map: 115

Summit Height (New height): 600.2m (converted to OSGM15, Leica GS15)

Summit Grid Reference: SH 72036 72323 (Leica GS15)

Bwlch Height: 547.2m (LIDAR)

Bwlch Grid Reference: SH 72647 72325 (LIDAR)

Drop: 53.0m (Leica GS15 summit and LIDAR bwlch)

Myrddyn Phillips and Aled Williams (January 2019)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Pen y Boncyn Trefeilw (SH 962 283) - 12th significant height revision

Survey post for Pen y Boncyn Trefeilw

There has been a Significant Height Revision to a hill that is listed in the Yr Uchafion and 600m Twmpau, with the summit height and drop of the hill being confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips on the 16^th August 2018. The summit of this hill was subsequently surveyed by Alan Dawson using a Leica RX1250 on the 24th November 2018, and it is this result that is given in the details for the hill at the end of this article.

Pen y Boncyn Trefeilw (SH 962 283)

The criteria for the two listings that this name change applies to are:

The name of the hill is Pen y Boncyn Trefeilw, and it is adjoined to the Y Berwyn range of hills, which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is positioned to the north of Llyn Efyrnwy (Lake Vyrnwy) and has the town of Y Bala towards the north north-west.

As the summit of the hill is not a part of designated open access land permission to visit should be sought, however the upper part of this hill is encircled by open access land and the summit of the hill is only a few metres from the boundary fence between this land and the grazing field where it is situated. Therefore common sense should prevail for those who want to visit.

Prior to the survey with the Trimble GeoXH 6000 this hill was listed with a 646m summit height, which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

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

The summit height produced by The Trimble GeoXH 6000 survey is 644.0m (643.953m to three decimal places) (converted to OSGM15), this is not a substantial height revision when compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

The Trimble GeoXH 6000 gathering data at the summit of Pen y Boncyn Trefeilw

Therefore, this hill’s new summit height is 644.0m (converted to OSGM15) and this was produced by surveying with the Trimble GeoXH 6000, this is 2.0m lower than its previously listed height of 646m which appears as a spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps. However, this new height is in accordance with the 5m contouring on OS Maps.

The above details have now been superseded by the Leica RX1250 survey conducted by Alan Dawson, and it is this summit result that is given below.

The full details for the hill are:

Group: Y Berwyn

Name: Pen y Boncyn Trefeilw

OS 1:50,000 map: 125

Summit Height (New height): 644.2m (converted to OSGM15)

Summit Grid Reference: SH 96250 28328

Bwlch Height: 588.4m (converted to OSGM15)

Bwlch Grid Reference: SH 97406 27854

Drop: 55.8m (Leica RX1250 summit and Trimble GeoXH 6000 bwlch)

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

Myrddyn Phillips and Aled Williams (January 2019)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Fan y Big (SO 036 206) - 11th significant height revision

1st survey post for Fan y Big

2nd survey post for Fan y Big

There has been a Significant Height Revision to a hill that appears in the following lists; Yr Uchafion, 700m Twmpau and Y Pellennig – The Remotest Hills of Wales, and which was initiated by LIDAR analysis conducted by Aled Williams followed by a survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips, with the latter conducted over two days on the 30^th June 2018 and the 21^st August 2018 in clear conditions turning to mist on the first survey and misty conditions clearing on the second survey.

LIDAR image of Fan y Big

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

Yr Uchafion – Welsh hills at or above 500m in height that have 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to the list appearing on Mapping Mountains on the 4^th November 2015.

700m Twmpau - Welsh hills at or above 700m and below 800m in height with 30m minimum drop, with an accompanying sub list entitled the 700m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 700m and below 800m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips.

The name of the hill is Fan y Big and it is placed in the central part of the main ridge that forms the Bannau Brycheiniog (Brecon Beacons) group of hills, which are situated in the South Wales Region (Region C, Sub-Region C2), and it is positioned between the towns of Aberhonddu (Brecon) to its north and Merthyr Tudful to its south.

The hill can be accessed from public footpaths originating from its north and from its south; or it can be combined as a longer expedition taking in the main Bannau Brycheiniog ridge either from its west or from its east.

Prior to LIDAR analysis and the subsequent survey with the Trimble GeoXH 6000 the height of the hill was listed as 719m based on the summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

Extract from the Ordnance Survey 1:125,000 Explorer map

The summit of this hill was surveyed three times over two days, each 53 days apart resulting in the following:

1^st survey 30.06.18: 716.800m

2^nd survey 30.06.18: 716.676m

3^rd survey 21.08.18: 716.754m

Average of three summit surveys: 716.746m

Therefore, the average of three summit surveys produced by the Trimble GeoXH 6000 is 716.7m (converted to OSGM15), this is not a dramatic height revision when compared to some survey results, 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 as surveyed with the Trimble GeoXH 6000 is 716.7m (converted to OSGM15) which is 2.3m lower than its previously listed height of 719m which appears on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The Trimble GeoXH 6000 gathering data at the summit of Fan y Big which resulted in this hill's significant height revision

The full details for the hill are:

Group: Bannau Brycheiniog

Summit Height (New height): 716.7m (converted to OSGM15)

Name: Fan y Big

OS 1:50,000 map: 16o

Summit Grid Reference: SO 03652 20658

Drop: 28.5m (converted to OSGM15)

For details on the 1st survey that significantly revised the summit height of this hill

For details on the 2nd survey that significantly revised the summit height of this hill

Myrddyn Phillips and Aled Williams (November 2018)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Banc y Foel (SN 725 186) - 10th significant height revision

Survey post for Banc y Foel

Significant Name Changes post for Banc y Foel

There has been a Significant Height Revision to a hill that appears in the Yr Uchafion and 500m Twmpau lists, and which was initiated by a survey with the Trimble GeoXH 6000 which was conducted on the 6^th May 2018 in good, clear conditions with hardly a breath of breeze.

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

500m Twmpau – Welsh hills at or above 500m and below 600m in height that have 30m minimum drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips.

The name of the hill is Banc y Foel and it is adjoined to the Mynydd Du range of hills, which are positioned in the western part of South Wales (Region C, Sub-Region C1). The hill is positioned with the A 4069 road to its east, and has the village of Llangadog towards the north and Brynaman towards the south.

Banc y Foel (SN 725 186)

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was estimated as c 536m based on a relatively large 530m uppermost contour ring on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

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

The summit height produced by The Trimble GeoXH 6000 survey is 531.6m (converted to OSGM15), this is a substantial height revision when compared to some revised heights, and comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or by LIDAR analysis, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by analysis of LIDAR. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Therefore, this hill’s new summit height is 531.6m (converted to OSGM15) and this was produced by surveying with the Trimble GeoXH 6000, this is 4.4m lower than its previously listed height of c 536m which was based on interpolation of the hill’s uppermost 530m ring contour on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Group: Mynydd Du

Name: Banc y Foel

OS 1:50,000 map: 160

Summit Grid Reference: SN 72536 18670

Summit Height (New height): 531.6m (converted to OSGM15)

Drop: 38.9m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Banc y Foel (SN 725 186) 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 2018)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Twyn Llech (SO 255 353) - 9th significant height revision

Survey post for Twyn Llech

Significant Name Changes post for Twyn Llech

Summit Relocation post for Twyn Llech

There has been a Significant Height Revision to a hill that appears in the Yr Uchafion and 700m Twmpau lists, and which was initiated by a survey with the Trimble GeoXH 6000, with the survey that resulted in this height revision being conducted on the 28^th September 2017 in good, clear conditions with just a breath of breeze.

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

Yr Uchafion – All Welsh hills at and above 500m in height that have 15m minimum drop. The list is co-authored by Myrddyn Phillips and Aled Williams, with the Introduction to the list appearing on Mapping Mountains on the 4^th November 2015.

700m Twmpau – All Welsh hills at and above 700m and below 800m in height that have 30m minimum drop, with the word Twmpau being an acronym standing for ‘thirty welsh metre prominences and upward’. The list is authored by Myrddyn Phillips.

The name of the hill is Twyn Llech and it is a part of the Mynyddoedd Duon (Black Mountains) range, which is an extensive group of hills in the south-eastern part of South Wales, and it is situated above and between the upper part of the Olchon Valley to its south-east and the Dyffryn Ewias (Vale of Ewyas) to its south. The hill is also situated between the small communities of Craswall towards its east and Capel-y-ffin towards its south, and the hill can be accessed from a car park just below the high point of Bwlch yr Efengyl (Gospel Pass) via the summit of Hay Bluff, or it can be approached from the south-east via paths leading to its southerly ridge from either the Olchon Valley and the Dyffryn Ewias (Vale of Ewyas).

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 706m based on the summit spot height which is positioned at approximately SO 25545 35372 (taken by using a ruler) on the Harvey 1:40,000 Offa’s Dyke South map. Whilst Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps give a summit spot height of 703m positioned at SO 25586 35010.

The Harvey maps 706m summit spot height

The Ordnance Survey 703m summit spot height

Two points were surveyed for summit position using the Trimble GeoXH 6000, one on the southerly point where the Ordnance Survey give their 703m spot height and one on the northerly point where Harvey maps give their 706m spot height. The summit area of this hill has two rises which complement these spot height positions and which have a slight dip in between.

The results produced by the Trimble GeoXH 6000 appear below:

Northerly high point: 703.639m (converted to OSGM15) at SO 25520 35383

Southerly high point: 702.721m (converted to OSGM15) at SO 25572 35032

The above result 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.

As the Harvey summit position was the one used for listing, it is the 706m spot height that this Significant Height Revisions post applies to.

The summit of this hill consists of tussock grass close to the main and now well maintained paved path that crosses this hill on a south – north direction, and therefore this hill’s new summit height as surveyed with the Trimble GeoXH 6000 is 703. 6m (converted to OSGM15) which is 2.4m lower than its previously listed height of 706m which appears on the Harvey 1:40,000 Offa’s Dyke South map.

The full details for the hill are:

Cardinal Hill: Twyn Llech

Summit Height (New height): 703.6m (converted to OSGM15)

Name: Twyn Llech

OS 1:50,000 map: 161

Summit Grid Reference: SO 25520 35383

Drop: 154.5m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Twyn Llech (SO 255 353) 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 (November 2017)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Bwlan (SH 946 255) - 8th significant height revision

Survey post for Bwlan

Hill Reclassifications post for Bwlan

There has been a Significant Height Revision initiated by analysis of LIDAR data by Aled Williams and which was subsequently confirmed by a survey with the Trimble GeoXH 6000 to a hill that was listed in the Yr Uchafion, with the survey that resulted in this height revision being conducted on the 4th May 2017.

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

Yr Uchafion - All Welsh hills at or above 500m in height that have 15m minimum drop.

500m Sub-Uchafion - All Welsh hills at or above 500m in height with 14m or more and less than 15m of drop. The list is co-authored by Myrddyn Phillips and Aled Williams.

The name of the hill is Bwlan and it is situated in the Y Berwyn range of hills which are in the south-eastern Sub-Region of North Wales (Region A, Sub-Region A4), with the hill being positioned between the stream valleys of the Afon Nadroedd and the Afon Eiddew, with both tumbling down in to Llyn Efyrnwy (Lake Vyrnwy) which is situated to the hill’s south-east.

The walk that took in the survey of this hill’s summit was conducted on a beautiful sunny day with a brisk easterly breeze, in the company of Aled Williams who had analysed this hill’s previous status as an Uchaf via LIDAR data.

The hill can be accessed from its north via a track that emerges from a conifer plantation and makes its way up to the area of the hill's bwlch, which is just north-west of the summit, however by far the best approach is from the south-east following a path either beside or above Pistyll Rhyd-y-meinciau, this is a series of waterfalls which are a part of the Afon Eiddew.

The addition of Bwlan to the Yr Uchafion was due to a basic levelling survey (BLS) conducted by Myrddyn Phillips on the 10.05.05, resulting in a 51ft 6˝ (15.7m) drop value, subsequently the hill has been deleted from the ranks of Yr Uchafion due to LIDAR data analysed by Aled Williams. LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales.

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

Bwlan

Summit Height: 526.1m

Summit Grid Reference: SH 94690 25541

Bwlch Height: 512.6m

Bwlch Grid Reference: SH 94180 25715

Drop: 13.55m

Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps give this hill a 528m summit spot height with the Ordnance Survey enlarged mapping hosted on the Geograph website giving a 514m spot height on the area of this hill’s bwlch.

The survey with the Trimble GeoXH 6000 produced a summit height of 525.9m (converted to OSGM15) and a bwlch height of 512.1m (converted to OSGM15) with the summit height coming 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, or a previous estimated summit height based on interpolation of contours. Also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised in favour of the 1:50,000 map for detailing these revisions.

The ground comprising the summit of this hill is easily distinguishable and comprises a mixture of grass and reed grass amongst a good sprinkling of moorland heather.

Therefore this hill’s new summit height is 525.9m (converted to OSGM15) which is 0.2m lower than the result produced by LIDAR data and 2.1m lower than the 528m spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill: Foel y Geifr

Summit Height (New Height): 525.9m (converted to OSGM15)

Name: Bwlan

OS 1:50,000 map: 125

Summit Grid Reference: SH 94692 25540

Drop: 13.8m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Bwlan (SH 946 255) which confirmed this hill's significant height revision

For details on the Hill Reclassification instigated from analysis of LIDAR data

For details on the subsequent survey that confirmed this hill's significant height revision

Myrddyn Phillips and Aled Williams (June 2017)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Moel Bowydd (SH 712 470) - 7th significant height revision

Survey post for Moel Bowydd

Hill Reclassifications post for Moel Bowydd

There has been a Significant Height Revision initiated by analysis of LIDAR data by Aled Williams and which was subsequently confirmed by a survey with the Trimble GeoXH 6000 to a hill listed in the Yr Uchafion, with the survey that resulted in this height revision being conducted on the 8th April 2017.

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

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

The name of the hill is Moel Bowydd and it is situated in the hills adjoined to the Arenig group in the northern part of the south-west Sub-Region of North Wales (Region A, Sub-Region A3), with the town of Blaenau Ffestiniog positioned to the south-west of the hill.

The walk that took in this hill’s summit was suggested by Aled who had analysed this hill’s Uchaf qualification via LIDAR data, and the walk and survey were conducted on a beautiful sunny day with hardly a breath of breeze.

The hill can be accessed via public footpaths from its west, east and south, with Blaenau Ffestiniog being a good starting point for an ascent; an alternate and longer ascent can start from above Llan Ffestiniog using a track beside the course of the Afon Teigl. However, the summit of this hill is not on designated open access land, therefore permission to visit should be sought, but as the summit is relatively close to a public footpath and with open access land to its immediate north, common sense should prevail and if wanting to visit the summit there is likely to be no objection to doing so.

The addition of Moel Bowydd to the list of Yr Uchafion was announced on Mapping Mountains on the 03.04.17, with its addition due to LIDAR data analysed by Aled Williams. LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales.

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

Moel Bowydd

Summit Height: 500.6m

Summit Grid Reference: SH 71276 47053

Bwlch Height: c 485m

Bwlch Grid Reference: SH 71586 47206

Drop: c 16m

Prior to analysis of LIDAR data the hill was not classified as contouring on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps implied it did not have the required height to qualify as an Uchaf, with Ordnance Survey maps giving this hill an uppermost 490m ring contour and bwlch contouring between 480m – 490m.

The survey with the Trimble GeoXH 6000 produced a summit height of 500.5m (converted to OSGM15) and a bwlch height of 482.4m (converted to OSGM15) with the summit height coming within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The summit of this hill is easily distinguishable and is positioned at the south-western end of a grassy ridge overlooking the Maen-offeren and Llechwedd quarries.

Therefore this hill’s new summit height is 500.5m (converted to OSGM15) which is 0.1m lower than the result produced by LIDAR data and 10.5m higher than the 490m uppermost ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill: Manod Mawr

Summit Height (New Height): 500.5m (converted to OSGM15)

Name: Moel Bowydd

OS 1:50,000 map: 115

Summit Grid Reference: SH 71272 47051

Drop: 18.1m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Moel Bowydd (SH 712 470) which when coupled with the analysis of LIDAR data resulted in this hill's significant height revision

For details on the Hill Reclassification instigated from analysis of LIDAR data and the subsequent survey that confirmed this hill's significant height revision

Myrddyn Phillips and Aled Williams (May 2017)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Craig Gwaun Taf (SO 005 207) - 6th significant height revision

Survey post for Craig Gwaun Taf

Hill Reclassifications post for Craig Gwaun Taf

There has been a Significant Height Revision initiated by analysis of LIDAR data by Joe Nuttall and a subsequent survey with the Trimble GeoXH 6000 to a hill listed in the Yr Uchafion, with the survey that resulted in this height revision being conducted on the 25th October 2016.

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

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

The name of the hill is Craig Gwaun Taf and it is situated in the hills of the Bannau Brycheiniog in the northern part of south Wales and the survey was conducted on a becalmed misty morning. The Bannau Brycheiniog are referred to in English as the Brecon Beacons and are positioned between the hills of Mynydd Epynt to their north and the hills of the south Wales valleys to their south.

Craig Gwaun Taf is situated between the high cwm that holds the infant Blaen Taf Fechan to its east and the busy A 470 road to its west and is positioned above the towns of Aberhonddu (Brecon) to its north north-east and Merthyr Tudful (Merthyr Tydfil) to its south south-east, and the hill can be easily accessed from the car park at Pont ar Daf to its south south-west with the path leading toward the bwlch just north of its summit; Bwlch Duwynt, being on the Beacons Way and one of the main paths leading to the summit of south Wales’ highest mountain; Pen y Fan.

The survey conducted with the Trimble GeoXH 6000 was due to communication with Joe Nuttall, who had analysed this hill’s summit and bwlch height with LIDAR data. LIDAR (Light Detection & Ranging) is highly accurate height data that is now freely available for much of England and Wales, and Joe has been diligently checking a number of hills for qualification to his parents 2,000ft list. These lists are based on a minimum 15m drop value and Joe found that LIDAR data gave Craig Gwaun Taf a drop of 15.783m.

However, if Craig Gwaun Taf has a minimum 15m of drop it would also be included in the listing of Welsh hills that has the working title of Yr Uchafion, with the introduction to this list being published on Mapping Mountains on the 4^th November 2015.

Craig Gwaun Taf is given an 824m summit spot height on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps that derives from the 2,704ft height on the series of old Six-Inch maps and has bwlch contouring between 800m – 810m, with an 815m spot height on the area of the bwlch on the Ordnance Survey enlarged mapping hosted on the Geograph website. These figures give this hill an approximate c 13m of drop based on interpolation of bwlch contours, or only 9m of drop if based on the 815m spot height. However, when Joe Nuttall analysed this hill with LIDAR data he found that it gave the summit as 825.885m and the bwlch as 810.102m, giving a drop value of 15.783m, which is sufficient for both Uchaf and Nuttall qualification.

The 826.4m (converted to OSGM15) height produced by the Trimble GeoXH 6000 is an average of three summit data sets and is 2.4m higher than the Ordnance Survey map height of 824m, and therefore comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised in favour of the 1:50,000 for detailing these revisions.

The summit of this hill is easily identified and consists of ground at the top of a grassy hummock a few metres east of the ridge path, and therefore this hill’s new summit height as surveyed by the Trimble GeoXH 6000 is 826.4m (converted to OSGM15) which is 2.4m higher than the current map height of 824m which appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill: Pen y Fan

Summit Height (New Height): 826.4m (converted to OSGM15)

Name: Craig Gwaun Taf

OS 1:50,000 map: 160

Summit Grid Reference: SO 00548 20720

Drop: 16.1m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data at the summit of Craig Gwaun Taf (SO 005 207) 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 (November 2016)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Mynydd yr Hewyrch (SH 816 150) - 5th significant height revision

Summit survey post for Mynydd yr Hewyrch

Bwlch survey post for Mynydd yr Hewyrch

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

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

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

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

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

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

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

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

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

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

The term Significant Height Revision applies to any listed hill whose Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised in favour of the 1:50,000 for detailing these revisions.

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

The full details for the hill are:

Cardinal Hill: Mynydd yr Hewyrch

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

Name: Mynydd yr Hewyrch

OS 1:50,000 map: 124, 125

Summit Grid Reference: SH 81697 15003

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

Dominance: 46.87%

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

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

Myrddyn Phillips and Aled Williams (November 2016)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Mynydd Ton (SS 949 940) - 4th significant height revision

2nd survey post for Mynydd Ton

1st survey post for Mynydd Ton

Summit Relocations post for Mynydd Ton

There has been a Significant Height Revision initiated by a survey conducted with the Trimble GeoXH 6000 to a hill listed in the Yr Uchafion and the 500m Twmpau (thirty welsh metre prominences and upward), with the survey that resulted in this height revision being conducted on the 23^rd July 2016.

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

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

500m Twmpau - All Welsh hills at or above 500m and below 600m in height with 30m minimum drop. The list is authored by Myrddyn Phillips.

The name of the hill is Mynydd Ton and it is situated in the Y Cymoedd range of hills in south Wales, and the survey was conducted on a warm and sunny afternoon in good, clear conditions. The Y Cymoedd are an extensive group of hills and comprise the area of the south Wales valleys.

Mynydd Ton is situated between Cwm Ogwr Fawr to its west and the Rhondda Fawr valley to its east and is positioned above the towns of Treorci (Treorchy) and Treherbert to its north and Nant-y-moel, Price Town and Ogmore Vale to its south-west, and the hill can be easily accessed from a track that leaves the A 4061 near to its high point and continues south-eastward to the north-western edge of a large conifer plantation, a path continues gaining the access point to a wide forest break which is relatively near the summit of the hill.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 539m at SS 94796 93958 with this position being beside an ancient cairn. This height was based on a 1,769.3ft surface height given on the Ordnance Survey Six-Inch map published in 1885. The 539m height was a relatively new addition to this hill’s listed height as its summit position was originally listed as ground beside its map heighted 535m triangulation pillar situated at SS 94931 94058.

The highest ground at the base of and beside the ancient cairn was surveyed with the Trimble GeoXH 6000 as being 534.2m (converted to OSGM15) high. This data set gave Estimated Accuracies of 5-15cm: 99.41% and a Standard Deviation of 0.0m with a margin of uncertainty for the height placement of the Trimble of 0.1m.

On my previous visit to this hill in February 2003 I judged ground approximately one minute's walk from the trig pillar to be slightly higher than ground at its base, and as the flush bracket adjoined to the trig pillar is given a height of 535.335m in the OS Trig Database it means that ground at its base is approximately 535m high. This figure is dependent upon the accuracy of the flush bracket height which is given as 3^rd order. Therefore the ground at the base of or near to the triangulation pillar is likely to be higher than that beside the ancient cairn; this is dependent upon the accuracy of the flush bracket height and the accuracy of the Trimble GeoXH 6000 survey.

The 534.2m (converted to OSGM15) height produced by the Trimble GeoXH 6000 is 4.8m lower than the previously listed height of 539m, which was based on the 1,769.3ft surface height on the 1885 Ordnance Survey Six-Inch map and therefore comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble. As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised in favour of the 1:50,000 for detailing these revisions.

The summit of this hill is easily identified and consists of ground at or near to the triangulation pillar, and therefore this hill’s new summit height is based on the 535m map height adjoined to the trig pillar, as the 534.2m (converted to OSGM15) result produced by the Trimble GeoXH 6000 for ground beside the ancient cairn at SS 94791 93954 is 4.8m lower than the hill’s previously listed height of 539m which appears as a 1,769.3ft imperial height on the Ordnance Survey Six-Inch map.

The full details for the hill are:

Cardinal Hill: Werfa

Summit Height (New Height): 534.4m (converted to OSGM15)

Name: Mynydd Ton

OS 1:50,000 map: 170

Summit Grid Reference: SS 94931 94059

Drop: 91.3m (converted to OSGM15)

The Trimble GeoXH 6000 gathering data beside the ancient cairn at the old summit position of Mynydd Ton which resulted in this hill's significant height revision

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

For details on the second survey of this hill

Myrddyn Phillips and Aled Williams (August 2016)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Crib y Rhiw (SH 663 248) - 3rd significant height revision

Summit survey post for Crib y Rhiw

Bwlch survey post for Crib y Rhiw

There has been a Significant Height Revision to a hill that is listed in the Y Pellennig, Welsh Highlands and the 600m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from separate Trimble GeoXH 6000 surveys conducted by Myrddyn Phillips and Aled Williams respectively.

The criteria for the listings this height revision affects appear below:

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

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

600m Twmpau - All Welsh hills at or above 600m and below 700m in height with 30m minimum drop. With the 600m Sub-Twmpau being all Welsh hills at or above 600m and below 700m in height with 20m or more and below 30m of drop. The word Twmpau is an acronym for thirty welsh metre prominences and upward and the list is authored by Myrddyn Phillips.

The name the hill is listed by is Crib y Rhiw and it is situated in the hills of the Rhinogydd which are positioned in the western part of North Wales. The summit survey was conducted on a warm and sunny day in the company of John Barnard and Graham Jackson, although they were not present during the survey, as John was inspecting the northerly top of this hill and Graham remained at the southerly connecting bwlch with our Leica GS15 that was gathering data to determine the drop value of Diffwys (SH 661 234). Whilst the bwlch was surveyed in January 2023 by Aled Williams with Rebecca Williams in attendance.

Crib y Rhiw is a relatively remote hill for Wales and it can be accessed on a traverse of the southern ridge of the Rhinogydd, either from Cwm Nantcol to the west or from the end of the paved road to the south which is situated above the small community of Bontddu.

The hill does not possess a summit spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and is given an uppermost contour of 670m on both of these maps, with the height resulting from the survey with the Trimble GeoXH 6000 being 681.3m (converted to OSGM15). Crib y Rhiw has a northerly top that has a 2,228ft (679.1m) height given it on the Ordnance Survey Six-Inch Map, and its previously listed height in the Y Pellennig, Yr Uchafion and 600m Twmpau was c 680m, which was based on the estimated height difference between the position of the Six-Inch Map height and the high point of the hill which is positioned on the southerly top.

The 681.3m (converted to OSGM15) height produced by the Trimble GeoXH 6000 is not a dramatic height revision when compared to the previously listed height of this hill of c 680m, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 681.3m (converted to OSGM15), and this is 1.3m higher than its previous c 680m estimated height and 10.3m higher than its uppermost ring contour on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Cardinal Hill: Y Llethr

Name: Crib y Rhiw

OS 1:50,000 map: 124

Summit Height (New Height): 681.3m (converted to OSGM15)

Summit Grid Reference: SH 66368 24868

Bwlch Height: 652.1m (converted to OSGM15)

Bwlch Grid Reference: SH 66080 25302

Drop: 29.2m

Gathering data at the summit of Crib y Rhiw which resulted in the significant height revision of this hill

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 - The Welsh 500m P15s (Yr Uchafion)

Llechog (SH 606 567) - 2nd significant height revision

Survey post for Llechog

There has been a Significant Height Revision to a hill that is listed in the Welsh Highlands – Uchafion Cymru and 700m Twmpau, 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.

Llechog (SH 606 567)

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

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

700m Twmpau - Welsh hills at or above 700m and below 800m in height that have 30m minimum drop, with an accompanying sub list entitled the 700m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 700m and below 800m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips and the details to it were published on Mapping Mountains on the 15^th April 2015.

700m Twmpau by Myrddyn Phillips

The name the hill is listed by is Llechog and it is adjoined to the Yr Wyddfa 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 A4086 road to its north-east and the A4085 road to its south-west, and has the village of Llanberis towards the north-west.

When the listing that later became known as the Welsh Highlands - Uchafion Cymru was first compiled this hill was listed with an estimated c 26m of drop, based on the 718m summit spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated c 692m bwlch height, based on interpolation of 10m contouring between 690m - 700m.

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

However, it was not until the Trimble GeoXH 6000 survey that the details for this hill could be accurately re-assessed. The summit height produced by this survey is 720.0m and is positioned at SH 60613 56751, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The Trimble GeoXH 6000 gathering data from the summit of Llechog

Therefore, the new listed summit height of this hill is 720.0mm and this was derived from a Trimble GeoXH 6000 survey, this is 2.0m higher than the previously listed summit height of 718m, which was based on the 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: Yr Wyddfa

Name: Llechog

OS 1:50,000 map: 115

Summit Height (New Height): 720.0m (converted to OSGM15)

Summit Grid Reference: SH 60613 56751

Bwlch Height: 692.1m (converted to OSGM15)

Bwlch Grid Reference: SH 60557 56634

Drop: 28.0m

Myrddyn Phillips and Aled Williams (August 2015)

Mapping Mountains - Significant Height Revisions - The Welsh 500m P15s (Yr Uchafion)

Twyn Walter (SN 828 175) - 1st significant height revision

Survey post for Twyn Walter

There has been a Significant Height Revision initiated by a survey conducted with the Trimble GeoXH 6000 to the listing of the Yr Uchafion and the 500m Twmpau (thirty welsh metre prominences and upward), with these details being retrospective as the survey that resulted in this height revision was conducted on 10^th July 2014.

The criteria for these listings appear below:

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

500m Twmpau - All Welsh hills at or above 500m and below 600m in height with 30m minimum drop. With the 500m Sub-Twmpau being all Welsh hills at or above 500m and below 600m in height with 20m or more and below 30m of drop. The list is authored by Myrddyn Phillips.

The name of the hill is Twyn Walter and it is situated in the Mynydd Du range of hills in south Wales, and the survey was conducted in the company of Mark Trengove on a lovely summer’s day when we visited the remotest point of mainland Wales as well as the remotest hill of mainland Wales.

The hill can be accessed from Glyntawe on a good path and track that ascends above the Dan-yr-Ogof Showcaves. Heading west beyond the hill is some of the remotest land in the whole of Wales with the southern land of Y Mynydd Du comprising hills with limestone outcrops and a great wilderness of open grassland, a visit is highly recommended.

The summit height of this hill has been dramatically decreased from its current Ordnance Survey 1:25,000 Explorer map height of 509m, with the survey conducted with the Trimble GeoXH 6000 giving the height of the hill as 502.1m (converted to OSGM15). Based on the 509m summit map height this hill used to be listed as a 500m Twmpau with over 30m of drop, however its height has now dramatically decreased and its drop value also re-evaluated giving this hill c 26m of drop and therefore it has been reclassified to a 500m Sub-Twmpau.

Therefore this hill’s new summit height is 6.9m lower than its previously listed height which came from the 509m spot height on current Ordnance Survey 1:25,000 Explorer maps and the Ordnance Survey enlarged mapping hosted on the Geograph website.

Since this height revision was announced the height and position of this hill's bwlch has been determined via LIDAR analysis conducted by Aled Williams, the details for which are given below.

The full details for the hill are:

Group: Mynydd Du

Name: Twyn Walter

OS 1:50,000 map: 160

Summit Height (New Height): 502.1m (converted to OSGM15)

Summit Grid Reference: SN 82837 17506

Bwlch Height: 475.9m (LIDAR)

Bwlch Grid Reference: SN 82597 17917 (LIDAR)

Drop: 26.25m (Trimble summit and LIDAR bwlch)

Gathering data from the summit of Twyn Walter 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)

Monday 9 October 2017

Mapping Mountains – Significant Height Revisions – Welsh Highlands - Uchafion Cymru

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