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

Pt. 510.0m (SH 819 314) 

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. 510.0m (SH 819 314)

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 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:

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 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.

 

ills of Wales, and are reproduced below@

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)