Mapping Mountains – Significant Height Revisions – 200m Twmpau

Comin Gwauncaegurwen (SN 721 131) 

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail produced by JoeNuttall in his surface analysis programme, with subsequent LIDAR analysis conducted by the DoBIH team and independently by Myrddyn Phillips. 

LIDAR image of Comin Gwauncaegurwen (SN 721 131)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

200m Twmpau 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, the A4069 road to its west and a minor road to its south-west, and has the village of Brynaman towards the north-west.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the main P30 list or the accompanying Hills to be surveyed sub list, as with no significant contours of note on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map it was difficult to judge whether any hill of note existed. 

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

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website 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 that was 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. 

Extract from the interactive mapping hosted on the WalkLakes 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 258m spot height is given on the summit area of this hill.  Latterly the contemporary Ordnance Survey 1:25,000 Explorer map now has an uppermost 250m contour for this hill. 

Extract from the contemporary online 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 Comin Gwauncaegurwen (SN 721 131)

LIDAR analysis gives the highest ground on this hill that could now be deemed natural as 258.4m positioned at SN 72135 13154, and when compared to detail on contemporary Ordnance Survey maps when the Welsh P30 lists were originated 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 258.4m and this was derived from LIDAR analysis, this is 34.4m higher than the uppermost 220m contour on the old Ordnance Survey 1:50,000 Landranger and 1:25,000 Outdoor Leisure map and 8.4m higher than the uppermost 250m contour that appears online on the contemporary 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 Gwauncaegurwen 

OS 1:50,000 map:  160

Summit Height (New Height):  258.4m (LIDAR) 

Summit Grid Reference:  SN 72135 13154 (LIDAR) 

Bwlch Height:  218.5m (LIDAR) 

Bwlch Grid Reference:  SN 72505 12523 (LIDAR) 

Drop:  39.9m (LIDAR) 

 

Myrddyn Phillips (March 2024)