Mapping Mountains – Hill Reclassifications – Y Trichant – The 300m Hills of Wales

Graig (SO 299 237) – Sub-Trichant reclassified to Trichant

There has been confirmation of a reclassification to the list of Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR summit image of Graig (SO 299 237)

The criteria for the list that this reclassification applies to are:

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 13th May 2017.

The name the hill is listed by is Graig and it is adjoined to the Mynyddoedd Duon group of hills which are situated in the eastern part of South Wales (Region C, Sub-Region C3), and it is positioned with minor roads to its west, south and east, with the A465 road further to its south-east, and has the small community of Cwmyoy towards the south.

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 Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for the main P30 list. 

When 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 an estimated c 28m of drop, based on an estimated c 346m summit height and an estimated c 318m bwlch height, with both based on interpolation of 10m contouring on the Ordnance Survey 1:25,000 Explorer map.

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

The details for this hill were re-examined when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping has many spot heights not on any other publicly available Ordnance Survey map and gives a 349m spot height on the summit area of this hill.  This spot height is also shown on Ordnance Survey data that appears on the Magic Maps website.  When coupled with the estimated c 318m bwlch height these values gave this hill c 31m of drop and the details of this hill’s new P30 status were subsequently posted on the RHB Yahoo Groups forum on the 30^th June 2013.

Extract from the Magic Maps website

During the re-assessment of this hill’s details the series of Ordnance Survey Six-Inch maps were examined and the origins of the 349m spot height can be traced back to the 1143.3ft (348.48m) surface height that appears on the 1887 map.

Extract from the series of Ordnance Survey Six-Inch maps

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 bwlch image for Graig

The confirmation of the reclassification of Graig from Sub-Trichant status is due to LIDAR analysis, resulting in a 348.4m summit height and a 318.0m bwlch height, with these values giving this hill 30.4m of drop which is sufficient for it to be classified as a Trichant.

The full details for the hill are:

Group:  Mynyddoedd Duon

Name:  Graig

OS 1:50,000 map:  161

Summit Height:  348.4m (LIDAR)

Summit Grid Reference:  SO 29983 23705 (LIDAR)

Bwlch Height:  318.0m (LIDAR)

Bwlch Grid Reference:  SO 30011 23797 (LIDAR)

Drop:  30.4m (LIDAR)

Myrddyn Phillips (January 2020)