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

 

Craig Nyth y Gigfran (SH 687 461) 

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 Nyth y Gigfran (SH 687 461)

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 Nyth y Gigfran 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 A470 road to its east and the A496 road to its south-east, and has the town of Blaenau Ffestiniog towards the east.

A basic levelling survey conducted by Myrddyn Phillips on the 30.08.04 gave this hill 43½ft (13.3m) of drop and the hill was therefore listed with an estimated c 529m summit height and an estimated c 516m bwlch height, with both heights based on the basic levelling survey and interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

Since the original compilation of this list there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites.

One of the mapping resources now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available maps and for this hill is has a 530m summit spot height. 

Extract from the interactive mapping hosted on the WalkLakes website

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 Nyth y Gigfran (SH 687 461)

LIDAR analysis gives the summit of this hill as 530.1m positioned at SH 68732 46178, 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 530.1m and this was derived from LIDAR analysis, this is 1.1m higher than the original estimated c 529m summit height and 10.1m higher than the uppermost 520m contour that appears on the contemporary Ordnance Survey 1:25,000 Explorer map and importantly this height signifies that an uppermost 530m 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 Nyth y Gigfran

OS 1:50,000 map:  115

Summit Height (New Height):  530.1m (LIDAR)

Summit Grid Reference:  SH 68732 46178 (LIDAR)  

Bwlch Height:  516.9m (LIDAR)

Bwlch Grid Reference:  SH 68649 46174 (LIDAR)

Drop:  13.2m (LIDAR)

 

Myrddyn Phillips and Aled Williams (June 2026)