Mapping Mountains – Summit Relocations – Y Trichant – The 300m Hills of Wales

Cefn (SN 997 734 & SN 997 733) 

There has been a Summit Relocation to a hill that is listed in the Y Trichant – The 300m Hills of Wales, 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 Cefn (SN 997 734 and SN 997 733)

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

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Cefn, and this was derived from the Tithe map, and it is adjoined to the Hirddywel group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B2), and it is positioned with minor roads to its north-west and south, and the B4518 road to its west, and has the village of Llanarmon (St Harmon) towards the south-west.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed under the point (Pt. 372m) notation with 28m of drop, based on the 372m summit spot height and the 344m bwlch spot height that appear 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.

LIDAR analysis gives the highest ground on this hill as 371.6m positioned at SN 99749 73389 and SN 99749 73392.  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 Cefn (SN 997 734 and SN 997 733)

The height produced by LIDAR analysis to the natural summit of this hill is 371.4m positioned at SN 99758 73405 and SN 99757 73402 and SN 99757 73398, and this position in relation to the raised field boundary 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 371.4m and this is positioned at SN 99758 73405 and SN 99757 73402 and SN 99757 73398, this is approximately 24 metres north-eastward from where the 372m spot height appears on the Ordnance Survey 1:25,000 Explorer map, and is approximately 18 metres north-eastward from where the high point of the raised field boundary is positioned. 

 

The full details for the hill are:

Group:  Hirddywel 

Name:  Cefn 

OS 1:50,000 map:  136, 147

Summit Height:  371.4m (LIDAR)                                                          

Summit Grid Reference (New Position):  SN 99758 73405 & SN 99757 73402 & SN 99757 73398 (LIDAR) 

Bwlch Height:  344.3m (LIDAR) 

Bwlch Grid Reference:  SO 00094 73404 (LIDAR) 

Drop:  27.2m (LIDAR) 

 

Myrddyn Phillips (January 2025)