Mapping Mountains – Significant Height Revisions – The Welsh P15s

 

Comin Gwauncaegurwen (SN 711 123) 

There has been a Significant Height Revision to a hill that is listed in The Welsh P15s, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Comin Gwauncaegurwen (SN 711 123)

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

The Welsh P15s – Welsh hills with 15m minimum drop, irrespective of their height, with an accompanying sub list entitled the Welsh Sub-P15s, with the criteria for this sub category being all Welsh hills with 14m or more and below 15m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list appearing on Mapping Mountains on the 10^th May 2019. 

The Welsh P15s by Myrddyn Phillips

The name the hill is listed by is Comin Gwauncaegurwen and this was derived from the Tithe map with the language protocol also used, and it is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A4068 road to its north-east, the A4069 road to its north-west and a minor road to its south, and has the village of Brynaman towards the north. 

Extract from the Ordnance Survey 1:50,000 Landranger map

When the listing that became known as The Welsh P15s was being compiled, this hill was not included in the main P15 list or the accompanying P14 sub list, as it possessed no contours of significance on either the Ordnance Survey 1:50,000 Landranger or the 1:25,000 Explorer map. 

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

Since the initial compilation of this list started there have been a number of Ordnance Survey 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 are current and digitally updated such as the mapping on the Magic Maps website.

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 a 216m spot height is given on the summit area of this hill. 

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 Comin Gawuncaegurwen (SN 711 123)

The summit height produced by LIDAR analysis is 216.6m and when compared to detail on the Ordnance Survey 1:50,000 Landranger and the 1:25,000 Explorer map, 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 216.6m and this was derived from LIDAR analysis.  This is 16.6m higher than the uppermost 200m contour on the contemporary Ordnance Survey 1:50,000 Landranger map and 26.6m higher than the uppermost 190m contour on the Ordnance Survey 1:25,000 Explorer map. 

 ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Mynydd Du 

Name:  Comin Gawuncaegurwen 

OS 1:50,000 map:  160

Summit Height (New Height):  216.6 (LIDAR)                                                           

Summit Grid Reference:  SN 71158 12343 (LIDAR) 

Bwlch Height:  196.6m (LIDAR) 

Bwlch Grid Reference:  SN 71330 12592 & SN 71332 12592 (LIDAR) 

Drop:  19.98m (LIDAR) 

 

Myrddyn Phillips (April 2024)