Mapping Mountains – Significant Height Revisions – 600m Twmpau and The Welsh Highlands – Uchafion Cymru

Craig Ysgafn (SH 659 443) 

There has been a Significant Height Revision to a hill that is listed in the 600m Twmpau and the 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 Craig Ysgafn (SH 659 443)

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 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 and is published on Mapping Mountains in Google Doc format.

600m Twmpau by Myrddyn Phillips

The 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.

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

The name the hill is listed by is Craig Ysgafn and it is adjoined to the Moelwyn Mawr group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A2), and it is positioned with the A4085 road to its west, the A487 road to its south and the A496 road to its east, and has the town of Blaenau Ffestiniog towards the east north-east.

When the list of Welsh 500m P15s that later became known as the The Welsh Highlands – Uchafion Cymru was first compiled, this hill was listed with an estimated c 26m of drop, based on the 689m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 663m bwlch height, based on interpolation of 10m contouring between 660m – 670m. 

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 Craig Ysgafn (SH 659 443)

LIDAR analysis gives the summit of this hill as 690.0m positioned at SH 65994 44332, and when compared to its originally listed summit height this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 690.0m and this was derived from LIDAR analysis, this is 1.0m higher than the originally listed summit height of 689m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map and importantly this height signifies that an uppermost 690m ring contour is missing from this map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Moelwyn Mawr

Name:  Craig Ysgafn

OS 1:50,000 map:  124

Summit Height (New Height):  690.0m (LIDAR)

Summit Grid Reference:  SH 65994 44332 (LIDAR)  

Bwlch Height:  663.4m (LIDAR)

Bwlch Grid Reference:  SH 66001 44596 (LIDAR)

Drop:  26.6m (LIDAR)

 

Myrddyn Phillips and Aled Williams (May 2026) 

Mapping Mountains – Significant Height Revisions – 600m Twmpau and Welsh Highlands – Uchafion Cymru

Pt. 631.7m (SH 733 622) 

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 – 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 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)

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. 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:

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

Therefore, the new listed summit height of this hill is 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.

 

ills of Wales, and are reproduced below@

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 – 600m Twmpau, The Welsh Highlands – Uchafion Cymru and Y Pellennig – The Remotest Hills of Wales

Cefn Dylif (SJ 089 369) 

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, and a subsequent Leica RX1250 survey conducted by Alan Dawson.

The summit of Cefn Dylif (SJ 089 369)

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

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

The name the hill is listed by is Cefn Dylif and it is adjoined to the Craig Berwyn group of hills, which are situated in the south-eastern part of North Wales (Region A, Sub-Region A3), 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, with a subsequent Leica RX1250 survey, resulting in a height of 618.5m.  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, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 618.5m and this was derived from a Leica RX1250 survey, this is 2.5m 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.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Craig Berwyn

Name:  Cefn Dylif

OS 1:50,000 map:  125

Summit Height (New Height):  618.5m (converted to OSGM15, Leica RX1250)

Summit Grid Reference:  SJ 08943 36943 (Leica RX1250)

Bwlch Height:  581.3m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SJ 09068 36590 (Trimble GeoXH 6000)  

Drop:  37.3m (Leica RX1250 summit and Trimble GeoXH 6000 bwlch)

 

Myrddyn Phillips and Aled Williams (June 2021)

 

  

Mapping Mountains – Significant Height Revisions – 600m Twmpau and The Welsh Highlands - Uchafion Cymru

Cnicht (SH 645 466)

There has been a Significant Height Revision to a hill that is listed in the 600m Twmpau and the 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.

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.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

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

The name the hill is listed by is Cnicht, and it is adjoined to the Moelwyn Mawr 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 A4085 road to its south-west, the A498 road to its north-west and the A470 road to its east, and has the small community of Croesor towards the south-west and the town of Blaenau Ffestiniog towards the east.

Prior to the Trimble GeoXH 6000 survey this hill was listed with an estimated c 106m of drop, based on the 689m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and an estimated c 583m bwlch height, based on interpolation of 10m contouring between 580m - 590m.

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

The Trimble GeoXH 6000 gathering data at the summit of Cnicht

Therefore, the new listed summit height of this hill is 690.7m and this was derived from a Trimble GeoXH 6000 survey.  This is 1.7m higher than its previously listed summit 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

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Moelwyn Mawr

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

Myrddyn Phillips and Aled Williams (July 2019)

Mapping Mountains – Significant Height Revisions – Yr Uchafion and 600m Twmpau

Foel Lwyd (SH 720 723)

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:

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.

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 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 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 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.

ills of Wales, and are reproduced below@

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)