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

Cefn Uchaf (SN 958 800) 

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 Uchaf (SN 958 800)

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 Uchaf, 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, with the A470 road farther to its north-west and the B4518 road farther to its east, and has the town of Llanidloes towards the north.

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

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 with 30m of drop, based on the 358m summit spot height positioned at SN 95816 80046 and the 328m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

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

However, it was not until a Trimble GeoXH 6000 survey and subsequent LIDAR analysis 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. 

Gathering data with the Trimble GeoXH 6000 on the summit area of Cefn Uchaf

There are a number of potential summit positions on this hill, with small outcrops of rock and other prominent undulations vying for the hill point.  Two positions were surveyed for summit position with the Trimble GeoXH 6000, with the highest coming to 357.4m positioned at SN 95873 80107, whilst LIDAR analysis gives the highest ground on this hill as 357.7m positioned at SN 95819 80021, and this position in relation to the spot height and also the highest Trimble GeoXH 6000 position 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. 

LIDAR summit image of Cefn Uchaf (SN 958 800)

Therefore, the summit height produced by LIDAR analysis is 357.7m and this is positioned at SN 95819 80021.  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 25 metres southward from where the 358m spot height appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, and approximately 86 metres south-westward from where the highest of the two Trimble GeoXH 6000 surveys was conducted. 

 

The full details for the hill are: 

Group:  Hirddywel 

Name:  Cefn Uchaf 

OS 1:50,000 map:  136

Summit Height:  357.7m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 95819 80021 (LIDAR) 

Bwlch Height:  329.3m (LIDAR) 

Bwlch Grid Reference:  SN 95421 80193 (LIDAR) 

Drop:  28.4m (LIDAR) 

 

Myrddyn Phillips (September 2025)