Mapping Mountains – Summit Relocations – 100m Twmpau

Cae Cefn (SO 315 009) 

There has been a Summit Relocation to a hill that is listed in the 100m 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 Cae Cefn (SO 315 009)

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

100m Twmpau - Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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. 

100m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cae Cefn and this was derived from the Tithe map, and it is adjoined to the Cefn yr Ystrad group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with minor roads to its west, south and east, and the A4042 road farther to its west, and has the town of Pont-y-pŵl (Pontypool) towards the west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with a 156m summit height, based on the spot height positioned on a road at SO 31429 00880 that appears on the Ordnance Survey 1:50,000 Landranger map. 

Extract from the Ordnance Survey 1:50,000 Landranger 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 Cae Cefn (SO 315 009)

LIDAR analysis gives the highest ground on this hill as 159.4m positioned at SO 31564 00957 and SO 31565 00959, and compared to its previously listed summit position 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 height produced by LIDAR analysis to the summit of this hill is 159.4m and is positioned at SO 31564 00957 and SO 31565 00959, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and is approximately 130 metres east north-eastward and positioned to a different feature from where the previously listed summit is positioned. 

 

The full details for the hill are: 

Group:  Cefn yr Ystrad 

Name:  Cae Cefn 

OS 1:50,000 map:  171

Summit Height:  159.4m (LIDAR) 

Summit Grid Reference (New Position):  SO 31564 00957 & SO 31565 00959 (LIDAR) 

Bwlch Height:  135.7m (LIDAR) 

Bwlch Grid Reference:  SO 31507 01161 (LIDAR) 

Drop:  23.7m (LIDAR) 

 

Myrddyn Phillips (March 2025)