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

 

Craig Ysgafn (SH 660 442) 

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 Craig Ysgafn (SH 660 442)

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

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.

Evaluating a summit and bwlch height for this hill based on contour interpolation from contemporary Ordnance Survey maps is difficult, as except for a 640m contour there is no significant independent contour of note 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 Craig Ysgafn (SH 660 442)

LIDAR analysis gives the summit of this hill as 658.2m positioned at SH 66008 44230, 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 658.2m and this was derived from LIDAR analysis, this is 18.2m higher than the uppermost 640m contour that appears on the contemporary Ordnance Survey 1:25,000 Explorer map and importantly this height signifies that an uppermost 650m 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):  658.2m (LIDAR)

Summit Grid Reference:  SH 66008 44230 (LIDAR)  

Bwlch Height:  647.9m (LIDAR)

Bwlch Grid Reference:  SH 66012 44249 (LIDAR)

Drop:  10.2m (LIDAR)

 

Myrddyn Phillips and Aled Williams (May 2026)