Mapping Mountains – Significant Height Revisions – The Welsh P15s

 

Ffridd Mathrafal (SJ 114 102) 

There has been a Significant Height Revision to a hill that is listed in 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 Ffridd Mathrafal (SJ 114 102)

The criteria for the list that this height revision 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 Ffridd Mathrafal, and this was derived from the Tithe map, and it is adjoined to the Esgeiriau Gwynion group of hills, which are situated in the southern part of North Wales (Region A, Sub-Region A3), and it is positioned with the A495 road to its immediate south, and has the town of Llanfair Caereinion towards the south south-west.

When the listing that became known as The Welsh P15s was being compiled, this hill was not included in the main P15 or Sub P14 list, as with an uppermost 140m ring contour and bwlch contouring between 130m – 140m that appear on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, it was deemed not to have sufficient prominence to be listed. 

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

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 for this hill a 148m summit spot height is given, with subsequent interpolation giving the hill an estimated c 13m of drop. 

Extract from the interactive mapping hosted on the WalkLakes website

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 Ffridd Mathrafal (SJ 114 102)

The summit height produced by LIDAR analysis is 150.0m and when compared to the details on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the WalkLakes map, this comes within the parameters of the Significant Height Revisions used within this page heading, and these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive 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 with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 150.0m and this was derived from LIDAR analysis.  This is 2.0m higher than the subsequently listed 148m summit heigth which was derived from the spot height that appears on the interactive WalkLakes map. 

 ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Esgeiriau Duon 

Name:  Ffridd Mathrafal 

OS 1:50,000 map:  125

Summit Height (New Height):  150.0m (LIDAR)                                                           

Summit Grid Reference:  SJ 11408 10233 (LIDAR)                                                  

Bwlch Height:  132.8m (LIDAR) 

Bwlch Grid Reference:  SJ 11315 10265 (LIDAR) 

Drop:  17.2m (LIDAR) 

 

Myrddyn Phillips (May 2025)