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

Pen Twmp (SM 988 329) – Dominant reclassified to Lesser Dominant

THIS HILL HAS SUBSEQUENTLY BEEN RECLASSIFIED BACK TO DOMINANT STATUS

There has been a reclassification to the listing of Y Trechol – The Dominant Hills of Wales due to data on the Ordnance Survey Interactive Coverage Map hosted on the Geograph website.  This reclassification is retrospective as it was initiated when data on this mapping was first analysed.

The criteria for this list are:

Y Trechol – The Dominant Hills of Wales - Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With an accompanying sub list entitled Y Trechol - The Lesser Dominant Hills of Wales, with the criteria for this sub category being those additional Welsh P30 hills whose prominence is 33% or more and below 50% of their absolute height.

During 2006 and 2007 drop values were added to the Welsh P30 lists that had been published on Geoff Crowder’s v-g.me website, this hill was then listed with an estimated c 110m of drop based on the 217m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 107m based on interpolation of bwlch contouring between 105m – 110m, with these values giving this hill 50.69% Dominance, and it was listed as such when this section of the Dominant list was completed in late January / early February 2012.

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

A locally known name of the hill is Pen Twmp and it is adjoined to the Mynydd Preseli group of hills, which are situated in the south-western part of Mid and West Wales (Region B, Sub-Region B4).  The hill is positioned with the A 40 road to its west and the B 4313 road to its north and has the Nant y Bugail to its south-west and the River Aer to its north-north-east, and has the town of Abergwaun (Fishguard) towards the north-west.

If wanting to visit the hill permission to do so should be sought as it is not a part of designated open access land, for those wishing to do so a public footpath passes to the west of the summit and can be accessed from either the north or south-west.

Shortly after Pen Twmp was first listed as a Dominant hill I was informed on how to access what is now known as the Ordnance Survey Interactive Coverage Map that is hosted on the Geograph website.  The larger scale interactive map on this website gives many spot heights that are not shown on other publicly available mapping, and when the details for this hill were analysed this map shows a 109m spot height on the area of this hill’s bwlch, and when coupled with the 217m summit spot height, these values gave the hill 108m of drop and 49.77% Dominance and it was therefore reclassified from a Dominant to a Lesser Dominant hill.

Extract from the Ordnance Survey Interactive Coverage Map hosted on the Geograph website

The full details for the hill are:

Group:  Mynydd Preseli

Name:  Pen Twmp

Dominance:  49.77%

OS 1:50,000 map:  157

Summit Grid Reference:  SM 988 329

Summit Height:  217m

Drop Summit to Bwlch:  108m

Drop Bwlch to ODN:  109m

Myrddyn Phillips (August 2018)