Mapping Mountains – Summit Relocations – 200m Twmpau

 

Pen y Ffridd (SJ 114 112) 

There has been a Summit Relocation to a hill that is listed in the 200m Twmpau, 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 Pen y Ffridd (SJ 114 112)

The criteria for the list that this summit relocation applies to are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

200m Twmpau by Myrddyn Phillips

The name the hill is listed by is Pen y Ffridd, 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 minor roads to its north-east and west, and the A495 road to its south-east, and has the village of Meifod towards the north-east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 218m summit height, based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

After the accompanying sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 41m of drop, based on the 218m summit spot height positioned at SJ 11499 11222 and an estimated c 177m bwlch height, based on interpolation of 10m contouring between 170m - 180m. 

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 analysis gives the highest ground on this hill as 219.8m positioned at SJ 11495 11219 and SJ 11488 11217.  However, this is a part of a raised field boundary and protocols dictate that as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill. 

LIDAR summit image of Pen y Ffridd (SJ 114 112)

The height produced by LIDAR analysis to the highest remaining natural ground on this hill is 219.6m and this is positioned at SJ 11492 11221, and 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 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 219.6m and this is positioned at SJ 11492 11221, this position is relatively close to where the spot height appears on the Ordnance Survey 1:25,000 Explorer map, and is approximately 3 metres north-westward from the high point of the raised field boundary. 

 

The full details for the hill are: 

Group:  Esgeiriau Gwynion 

Name:  Pen y Ffridd 

OS 1:50,000 map:  125

Summit Height:  219.6m (LIDAR) 

Summit Grid Reference (New Position):  SJ 11492 11221 (LIDAR) 

Bwlch Height:  173.0m (LIDAR) 

Bwlch Grid Reference:  SJ 10462 11208 (LIDAR) 

Drop:  46.65m (LIDAR) 

 

Myrddyn Phillips (January 2025)