Mapping Mountains – Summit Relocations – The Welsh P15s

Mynydd Aberysgir (SN 985 312) 

There has been a Summit Relocation to a hill that is listed in the 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 Mynydd Aberysgir (SN 985 312)

The criteria for the list that this summit relocation 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 Mynydd Aberysgir, and this was derived from the Tithe map, and it is adjoined to the Mynydd Epynt group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads with the A40 road farther to its south, and has the town of Aberhonddu (Brecon) towards the east south-east.

When the listing that became known as The Welsh P15s was being compiled, this hill was included in the main list with an estimated c 18m of drop, based on the 341m twin summit spot heights positioned at SN 98586 31211 on the Ordnance Survey 1:25,000 Explorer map and SN 98676 31149 on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, and an estimated c 323m bwlch height based on interpolation of 10m contouring between 320m – 330m. 

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. 

LIDAR summit image of Mynydd Aberysgir (SN 985 312)

LIDAR analysis gives the highest ground on this hill as 341.1m positioned at SN 98578 31205 which corresponds to the position of the spot height that appears on the Ordnance Survey 1:25,000 Explorer map, with LIDAR also giving 340.8m positioned at SN 98676 31157 which corresponds to the position of the spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.  As LIDAR analysis has de-twinned the summit of this hill this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or the de-twinning of a summit, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Therefore, the summit height produced by LIDAR analysis is 341.1m and is positioned at SN 98578 31205, this position corresponds to the spot height on the contemporary Ordnance Survey 1:25,000 Explorer map and is approximately 100 metres north-westward from the position of the previously listed twin summit at the spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

 

The full details for the hill are: 

Group:  Mynydd Epynt 

Name:  Mynydd Aberysgir 

OS 1:50,000 map:  160

Summit Height:  341.1m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 98578 31205 (LIDAR) 

Bwlch Height:  321.4m (LIDAR) 

Bwlch Grid Reference:  SN 98385 31519 & SN 98384 31522 (LIDAR) 

Drop:  19.7m (LIDAR) 

 

Myrddyn Phillips (May 2025)