Mapping Mountains – Hill Reclassifications – Y Trechol – The Dominant Hills of Wales

Pen y Ddinas (SN 627 357) – Lesser Dominant addition

There has been an addition to the listing of Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, dominance and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pen y Ddinas (SN 627 357)

The criteria for the list that this addition applies to are:

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Pen y Ddinas and it is adjoined to the Mynydd Pencarreg group of hills, which are situated in the south-western part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north, the B4337 road to its south-west and the B4302 road to its east, and has the village of Llansawel towards the north-west.

When the original 200m height band of Welsh P30 hills published on Geoff Crowder’s v-g.me website were standardised and interpolated heights and drop values also included the details for this hill were re-evaluated, and it was listed with an estimated c 53m drop, based on an estimated c 207m summit height and an estimated c 154m bwlch height, with both heights based on interpolation of 10m contouring that appear on the contemporary Ordnance Survey 1:25,000 Explorer map. 

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and for this hill it had a 155m bwlch spot height and when coupled with a re-evaluation of its estimated summit height of c 203m , these values gave this hill an estimated c 48m of drop, which was still insufficient for Lesser Dominant status.

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.

Therefore, the addition of this hill to Lesser Dominant status is due to LIDAR analysis, resulting in a 230.9m summit height and a 153.2m bwlch height, with these values giving this hill 77.7m of drop and 33.63% dominance, which is sufficient for it to be classified as a Lesser Dominant hill.

 

The full details for the hill are:

Group:  Mynydd Pencarreg

Name:  Pen y Ddinas

OS 1:50,000 map:  146

Summit Height:  230.9m (LIDAR)

Summit Grid Reference:  SN 62756 35746 (LIDAR)

Bwlch Height:  153.2m (LIDAR)

Bwlch Grid Reference:  SN 62239 35477 (LIDAR)

Drop:  77.7m (LIDAR)

Dominance:  33.63% (LIDAR)

 

Myrddyn Phillips (June 2022)