Mapping Mountains – Hill Reclassifications – The Welsh P15s

 

Cae Cefn Issa (SN 692 009) – 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 LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Cae Cefn Issa (SH 692 009)

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 Cae Cefn Issa, and this was derived from the Tithe map, and it is adjoined to the Tarren y Gesail group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with the A493 road to its south, and has the town of Machynlleth 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 list or the accompanying sub list, and was subsequently documented with an estimated c 13m of drop, based on an estimated c 120m summit height and an estimated c 107m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the 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.

Therefore, the addition of this hill to Welsh P15 status is due to LIDAR analysis, resulting in a 119.5m summit height and a 103.9m bwlch height, with these values giving this hill 15.5m 0f drop, which is sufficient for it to be classified as a Welsh P15. 

 

The full details for the hill are: 

Group:  Tarren y Gesail 

Name:  Cae Cefn Issa 

OS 1:50,000 map:  135

Summit Height:  119.5m (LIDAR)                                                           

Summit Grid Reference:  SH 69202 00955 (LIDAR)                                                  

Bwlch Height:  103.9m (LIDAR) 

Bwlch Grid Reference:  SH 69081 01055 (LIDAR) 

Drop:  15.5m (LIDAR) 

 

Myrddyn Phillips (December 2025)