Mapping Mountains – Hill Reclassifications – The Welsh P15s

 

Pen Las Rock (SH 208 815) – Welsh P15 addition

There has been an addition to the list of The Welsh P15s, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data. 

The criteria for the list that this addition 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 Pen Las Rock and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is positioned with the coast to its immediate west and a minor road to its north-east, and has the town of Caergybi (Holyhead) towards the east. 

When the listing that became known as The Welsh P15s was being compiled, this hill was not included in either the main P15 list or the accompanying P14 sub list, as the contours that appear on the Ordnance Survey 1:25,000 Explorer map are hard to decipher. 

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

Since the start of this list’s compilation 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 old Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and the interactive mapping on the Magic Maps website. 

The details for this hill were re-assessed against the large scale mapping that has replaced the Ordnance Survey mapping available on the Geograph website and the interactive mapping available of the Magic Maps website.  The former gives this hill a 50m summit spot height and the latter a 49m summit spot height.  The 50m spot height compliments 5m contouring available online, with this also giving bwlch contouring between 30m – 35m and which has been estimated as c 33m in height. 

Extract from the Ordnance Survey mapping hosted on the Geograph website 

Therefore, the addition of this hill to Welsh P15 status is due to detail on contemporary maps produced from Ordnance Survey data, resulting in a 50m summit height and an estimated c 33m bwlch height, with these values giving this hill an estimated c 17m 0f drop, which is sufficient for it to be classified in the main list of The Welsh P15s. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Pen Las Rock 

OS 1:50,000 map:  114

Summit Height:  50m (spot height)                                                           

Summit Grid Reference:  SH 20813 81594 (spot height) 

Bwlch Height:  c 33m (interpolation) 

Bwlch Grid Reference:  SH 20829 81624 (interpolation) 

Drop:  c 17m (spot height summit and interpolated bwlch) 

 

Myrddyn Phillips (October 2021)