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

Thursday 5 October 2017

Mapping Mountains – Significant Height Revisions – Y Pellennig –The Remotest Hills of Wales

Y Pellennig –The Remotest Hills of Wales – Significant Height Revisions

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, with the Change Register to this list available via Mapping Mountains.

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 this list appear below presented chronologically in receding order.

Mapping Mountains - Significant Height Revisions - Y Pellennig - The Remotest Hills of Wales

Foel Fras (SH 696 681) - 11th 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 – 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

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 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, the Leica RX1250 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, Leica RX1250 or by LIDAR analysis.

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 - Y Pellennig - The Remotest Hills of Wales

Carreg Rhoson (SM 672 256) - 10th significant height revision

There has been a Significant Height Revision to a hill that is listed in the 30-99m Twmpau and the 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 detail on the DataMapWales.

Carreg Rhoson (SM 672 256 - the island on the right

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

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

30-99m Twmpau by Myrddyn Phillips

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

The name the hill is listed by is Carreg Rhoson, and it is adjoined to the Garn Fawr group of hills which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it forms a part of the islet chain known as Carreg Rhoson, and is positioned to the west of the Pembrokeshire coast, with the small city of Tyddewi (St David’s) towards the east.

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the main P30 list as the small uppermost 30m ring contour that appears on the Ordnance Survey 1:25,000 Explorer map had been missed.

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 30m summit height, based on interpolation of its uppermost 30m ring contour. As this hill is the high point of an island it was also listed with an estimated c 30m drop.

Extract from the DataMapWales

However, it was not until the DataMapWales became available online that the details of this hill could be checked against a product viewed as being more accurate than the contouring on the contemporary Ordnance Survey 1:25,000 Explorer map. This mapping has a 28m spot height for this hill and this is similar to the 27.42m summit height produced by the surface analysis programme developed by Joe Nuttall (JNSA) that uses the OS Terrain product where LIDAR coverage is not available, 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 28m and this was derived from detail on the DataMapWales, this is 2m lower than the previously listed summit height of c 30m, which was based on interpolation of its uppermost 30m ring contour that appears on the Ordnance Survey 1:25,000 Explorer.

The full details for the hill are:

Group: Garn Fawr

Name: Carreg Rhoson

OS 1:50,000 map: 157

Summit Height: 28m (spot height)

Summit Grid Reference: SM 67228 25658 (JNSA)

Bwlch Height: N/A (island)

Bwlch Grid Reference: N/A (island)

Drop: 28m (spot height)

Remoteness: 5.175km (JNSA)

Myrddyn Phillips and Aled Williams (July 2024)

Mapping Mountains - Significant Height Revisions - Y Pellennig - The Remotest Hills of Wales

Pt. 714.3m (SH 627 359) - 9th 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

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 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 - Y Pellennig - The Remotest Hills of Wales

Ffridd Ddu (SH 726 064) - 8th significant height revision

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

LIDAR image of Ffridd Ddu (SH 726 064)

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

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

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

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

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

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

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

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

Extract from the interactive mapping hosted on the WalkLakes website

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

LIDAR summit image of Ffridd Ddu (SH 726 064)

LIDAR analysis gives the highest ground on this hill as 435.0m positioned at SH 72667 06467, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

Therefore, the new listed summit height of this hill is 435.0m and this was derived from LIDAR analysis, this is 2.0m higher than the previously listed height of 435m which was based on the spot height that appeared on Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

The full details for the hill are:

Group: Tarren y Gesail

Name: Ffridd Ddu

OS 1:50,000 map: 124

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

Summit Grid Reference: SH 72667 06467 (LIDAR)

Bwlch Height: 413.0m (LIDAR)

Bwlch Grid Reference: SH 72593 06527 (LIDAR)

Drop: 22.0m (LIDAR)

Remoteness: 2.590km

Myrddyn Phillips and Aled Williams (July 2023)

Mapping Mountains - Significant Height Revisions - Y Pellennig - The Remotest Hills of Wales

Cefn Dylif (SJ 089 369) - 7th 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:

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.

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 - Y Pellennig - The Remotest Hills of Wales

Pt. 22.2m (SM 701 226) - 6th significant height revision

Hill Reclassifications post for Pt. 22.2m

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

Pt. 22.2m (SM 701 226)

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

30-99m Twmpau - Welsh hills at or above 30m and below 100m in height with 30m minimum drop, this height band of hills has two accompanying sub lists, the first of which is entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m in height with 20m or more and below 30m of drop, and the second sub category which this hill is a part of is entitled the Double Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 20m and below 30m 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. This list is authored by Myrddyn Phillips.

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 a joint compilation between 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 the Mapping Mountains site in Google Doc format.

As the authors do not know an appropriate name for this hill either from historic research or local enquiry it is being listed by the point (Pt. 22.2m) notation, and it is adjoined to the Carn Llidi group of hills which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4), and it is positioned in a small sheltered bay on the southern side of Ynys Dewi.

This hill did not appear in the accompanying Hills to be surveyed sub list when the original Welsh 30-99m P30 hills were published on Geoff Crowder’s v-g.me website, as it did not meet the criteria then used for this sub category, however this sub list has now been standardised, with interpolated drop values and interpolated summit heights also included.

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

Even when this sub list was standardised contemporary Ordnance Survey 1:25,000 Explorer maps do not give the hill any contour ring. The lack of contour rings is also applicable to the Ordnance Survey Vector Map Local hosted on the Geograph website which is entitled the Interactive Coverage Map.

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

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 has 5m contour intervals, and this mapping gives this hill an uppermost 15m ring contour.

Extract from the OS Maps website

The summit height produced by LIDAR analysis is 22.2m, this height comes within the parameters of the Significant Height Revisions used within this page heading, and 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.

LIDAR image of Pt. 22.2m, 1m contour (black), 10m contour (red) and sea level (yellow)

Close up LIDAR image of Pt. 22.2m, 1m contour (black), 10m contour (red) and sea level (yellow)

Therefore, this hill’s new listed summit height is 22.2m and this was derived from LIDAR analysis conducted by Aled Williams, this is 22.2m higher than information on the Ordnance Survey 1:25,000 Explorer map and 7.2m higher than the uppermost 15m contour ring on the OS Maps website.

The full details for the hill are:

Group: Carn Llidi

Name: Pt. 22.2m

OS 1:50,000 map: 157

Summit Height (New height): 22.2m (LIDAR)

Summit Grid Reference: SM 70180 22696 (LIDAR)

Bwlch Height: N/A, sea level

Bwlch Grid Reference: N/A, sea level

Drop: 22.2m (LIDAR)

Remoteness: 3.400km

Myrddyn Phillips and Aled Williams (June 2019)

Mapping Mountains - Significant Height Revisions - Y Pellennig - The Remotest Hills of Wales

Whiteford Burrows (SS 448 964) - 5th significant height revision

Hill Reclassifications post for Whiteford Burrows

There has been a Significant Height Revision to a hill that now appears in the Y Pellennig – The Remotest Hills of Wales list due to LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips.

LIDAR image of Whiteford Burrows

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

The name of the hill is Whiteford Burrows and it is adjoined to the Gŵyr group of hills, which are situated in the western part of South Wales (Region C, Sub-Region C1), and it is positioned overlooking Whiteford Point and the coast, and has the small community of Llanmadog towards the south.

As the hill is a part of designated open access land it can be approached from any direction, for those wishing to visit the Wales Coast Path approaches the hill from the south and follows land close to the coast and heads toward Whiteford Point, and the summit of the hill is only a short distance from this long distance path.

Prior to LIDAR analysis this hill was not catalogued as the uppermost contour given it on the Ordnance Survey 1:25,000 Explorer map is 5m, whilst the Ordnance Survey 1:50,000 Landranger map has no contours. LIDAR gives a summit height of 28.3m, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

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

Therefore, this hill’s new summit height is 29.6m and this was produced by LIDAR analysis, this is 24.6m higher than the uppermost 5m contour on the Ordnance Survey 1:25,000 Explorer map, however this new height is in accordance with the 5m contouring on OS Maps.

LIDAR summit image of Whiteford Burrows

The full details for the hill are:

Group: Gŵyr

Name: Whiteford Burrows

OS 1:50,000 map: 159

Summit Height (New height): 29.6m (LIDAR)

Summit Grid Reference: SS 44870 96422 (hand-held GPS)

Bwlch Height: 9.2m (LIDAR)

Bwlch Grid Reference: SS 44631 95701 (LIDAR)

Drop: 20.4m (LIDAR)

Remoteness: 2.925km

Myrddyn Phillips and Aled Williams (December 2018)

Mapping Mountains - Significant Height Revisions - Y Pellennig - The Remotest Hills of Wales

Fan y Big (SO 036 206) - 4th 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 - Y Pellennig - The Remotest Hills of Wales

Emsger (SM 651 226) - 3rd significant height revision

Survey post for Emsger

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

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

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

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

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

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

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

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

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

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

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

The full details for the hill are:

Cardinal Island: Bishops and Clerks

Summit Height: 33.8m (converted to OSGM15)

Name: Emsger

OS 1:50,000 map: 157

Summit Grid Reference: SM 65116 22619

Drop: 33.8m (converted to OSGM15)

Dominance: 100.00%

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

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

Myrddyn Phillips and Aled Williams (June 2016)

Mapping Mountains - Significant Height Revisions - Y Pellennig - The Remotest Hills of Wales

Ynys Arw (SH 266 945) - 2nd significant height revision

Survey post for Ynys Arw

Hill Reclassifications post for Ynys Arw

There has been a Significant Height Revision to a hill that is listed in the Y Pellennig - The Remotest Hills of Wales which was initiated by a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted on the 13^th September 2015.

The criteria for this list 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.

The name of the hill is Ynys Arw and it forms one of the islands that make up the archipelago of Ynysoedd y Moelrhoniaid (The Skerries), these islands are positioned to the north-west of Ynys Môn (Anglesey).

Ynys Arw is the most south-westerly island of this archipelago and has two high points, with the more southerly of these being the highest. As Ynys Arw is a tidal island it is connected to its higher neighbour at high tide, the higher island is where The Skerries Lighthouse is situated and is the highest point of the archipelago and is also listed as a Pellennig hill.

The survey of this hill was suggested by Rob Woodall and it was conducted late in the afternoon. Twelve of us visited Ynysoedd y Moelrhoniaid in a Rib using a company named RibRide who are based at the Holyhead Marina during the summer months, and the trip cost £35.00 per person.

The summit of Ynys Arw is easily accessed at low tide from the Lighthouse, although hands on rock are required to get down to the wet land between it and the higher island. This connecting land is cut off from the higher island at high tide. The ascent from the connecting land is initially over wet rock and then grass which has a multitude of burrowed Tern nests excavated into it.

The island of Ynys Arw was not classified in any list prior to the survey with the Trimble GeoXH 6000 as it is given an uppermost contour of only 10m on Ordnance Survey 1:25,000 Explorer maps. It was surveyed with the Trimble GeoXH 6000 at being 15.2m (converted to OSGM15) high.

The 15.2m (converted to OSGM15) height produced by the Trimble GeoXH 6000 is not a dramatic height revision when compared to an estimated c 12m height for this island’s summit based on contour interpolation taken from its uppermost 10m map ring contour, but as the contours on the Ordnance Survey 1:25,000 Explorer map are at 5m intervals 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 this hill’s new summit height is 15.2m (converted to OSGM15) which is 3.2m higher than the previously estimated height and 5.2m higher than its uppermost ring contour on Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Island: Ynysoedd y Moelrhoniaid

Summit Height (New Height): 15.2m (converted to OSGM15, Trimble GeoXH 6000)

Name: Ynys Arw

OS 1:50,000 map: 114

Summit Grid Reference: SH 26647 94598 (Trimble GeoXH 6000)

Drop: 15.2m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Gathering data from the summit of Ynys Arw which resulted in this island's significant height revision

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

Myrddyn Phillips and Aled Williams (October 2015)

Mapping Mountains - Significant Height Revisions - Y Pellennig - The Remotest Hills of Wales

Crib y Rhiw (SH 663 248) - 1st 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:

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)

Thursday 5 October 2017

Mapping Mountains – Significant Height Revisions – Y Pellennig –The Remotest Hills of Wales

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