Mapping Mountains – Significant Height Revisions – 500m Twmpau, Y Trechol – The Dominant Hills of Wales and The Welsh Highlands – Uchafion Cymru

 

Yr Eifl (SH 364 447) 

There has been a Significant Height Revision that is retrospective to a hill that is listed in the 500m Twmpau, Y Trechol – The Dominant Hills of Wales and the The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop, the dominance 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. 

Yr Eifl (SH 364 447)

The criteria for the three 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

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

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The 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 Yr Eifl and it is adjoined to its own group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with minor roads to its north-east, the B4417 road to its south and the A499 road to its east, and has the villages of Trefor towards the north north-east and Llithfaen towards the south south-west.

When the listings of the 500m Twmpau, Y Trechol – The Dominant Hills of Wales and The Welsh Highlands – Uchafion Cymru were first compiled, this hill was listed with a summit height of 564m, based on the spot height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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

However, it was not until the survey with the Leica GS15 that the details for this hill could be accurately re-assessed.  Although the trig pillar is positioned on a relatively stable base it is positioned on the top of a substantial ancient cairn which consists of a multitude of individual stones and rocks and as this is considered as not being permanent in nature, it is the highest remaining natural ground on the periphery of the ancient cairn that is taken as both its listed summit height and summit position, and when compared to its originally listed summit height of 564m this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Gathering data with the Leica GS15 at the listed summit position of Yr Eifl

Therefore, the new listed summit height of this hill is 560.7m and this was derived from a Leica GS15 survey, this is 3.3m lower than the originally listed summit height of 564m, which was based on the spot height adjoined to a triangulation pillar 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:  Yr Eifl

Name:  Yr Eifl

OS 1:50,000 map:  123

Summit Height (New Height):  560.7m (converted to OSGM15, Leica GS15)

Summit Grid Reference:  SH 36482 44734 (Leica GS15)  

Bwlch Height:  129.4m (LIDAR)

Bwlch Grid Reference:  SH 45347 48678 (LIDAR)

Drop:  431.3m (Leica GS15 summit and LIDAR bwlch)

Dominance:  76.92% (Leica GS15 summit and LIDAR bwlch)

 

Myrddyn Phillips and Aled Williams (February 2026)

Mapping Mountains – Significant Height Revisions – 500m Twmpau and Welsh Highlands – Uchafion Cymru

 

Foel Ganol (SH 687 715) 

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:

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 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.

 

ills of Wales, and are reproduced below@

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 – 500m Twmpau and Welsh Highlands – Uchafion Cymru

 

Tryfan (SH 596 580) 

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. 

Tryfan (SH 596 580)

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 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:

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 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.

 

ills of Wales, and are reproduced below@

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 – 500m Twmpau and Welsh Highlands – Uchafion Cymru

Tryfan (SH 597 578) 

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. 

Tryfan (SH 597 578)

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 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 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:

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 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.

 

ills of Wales, and are reproduced below@

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)