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

 

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

Pt. 914.9m (SH 659 585) - 36th significant height revision

Survey post for Pt. 914.9m

Hill Reclassifications post for Pt. 914.9m

 

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 a Trimble GeoXH 6000 survey conducted by Aled Williams. 

Pt. 914.9m (SH 659 585).  Photo: Aled Williams

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

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. 914.9m) notation, 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 initial P10 sub list was completed in June 2020 this hill was listed with 9.4m of drop, based on a 31ft basic levelling survey conducted by Myrddyn Phillips on the 02.05.99.  However, with no significant independent contour of note on the contemporary Ordnance Survey 1:25,000 Explorer map it was difficult to give this hill an accurate summit height. 

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

The hill was subsequently analysed via LIDAR by Aled Williams, resulting in a 913.9m summit height and a 905.1m bwlch height, with these values giving this hill 8.8m of drop, which was insufficient for it to be classified as a Welsh Highland Sub.  However, with the drop value relatively close to the qualifying criterion of 10m this hill was prioritised for a survey with the Trimble GeoXH 6000. 

The Trimble GeoXH 6000 gathering data at the summit of Pt. 914.9m (SH 659 585).  Photo: Aled Williams

The Trimble GeoXH 6000 survey gives the summit of this hill as 914.9m positioned at SH 65981 58563, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

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

Therefore, the new listed summit height of this hill is 914.9m and this was derived from a Trimble GeoXH 6000 survey, this is 14.9m higher than the uppermost 900m contour that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Glyder Fawr

Name:  Pt. 914.9m           

OS 1:50,000 map:  115

Summit Height (New Height):  914.9m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 65981 58563 (Trimble GeoXH 6000)

Bwlch Height:  904.4m (converted to OSGM15, Trimble GeoXH 6000)

Bwlch Grid Reference:  SH 65982 58556 (Trimble GeoXH 6000)   

Drop:  10.5m (Trimble GeoXH 6000) 

 

Aled Williams and Myrddyn Phillips (November 2024)