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

 

Gorn Hill (SN 968 844) 

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 Gorn Hill (SN 968 844)

The criteria for the list that this summit relocation 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 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 listed by is Gorn Hill, 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 the A470 road to its north and a minor road to its south, and has the town of Llanidloes towards the west.

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 main P30 list with a 326m summit height, based on the spot height positioned at SN 96892 84574 that appears on the contemporary 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 summit image of Gorn Hill (SN 968 844)

LIDAR analysis gives the highest ground on this hill as 326.4m positioned at SN 96895 84496, and this in relation to the previously listed summit position which LIDAR analysis gives as 326.1m in height and positioned at SN 96896 84576 and SN 96896 84575 and SN 96898 84575 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. 

Extract from the DataMapWales interactive mapping

Therefore, the summit height produced by LIDAR analysis is 326.4m and this is positioned at SN 96895 84496, 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 78 metres southward from where the previously listed summit and the spot height is positioned and importantly the new summit position is placed in a different contour on the DataMapWales interactive mapping. 

 

The full details for the hill are:

Group:  Hirddywel 

Name:  Gorn Hill 

OS 1:50,000 map:  136

Summit Height:  326.4m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 96895 84496 (LIDAR) 

Bwlch Height:  278.1m (LIDAR) 

Bwlch Grid Reference:  SN 97747 83851 & SN 97747 83848 (LIDAR) 

Drop:  48.3m (LIDAR) 

 

Myrddyn Phillips (November 2024)