Mapping Mountains – Summit Relocations – Y Pedwarau – The 400m Hills of Wales

Gїas (SN 864 861)

There has been a Summit Relocation to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales, with the summit height and its position confirmed via LIDAR analysis conducted by Aled Williams.

LIDAR image of Gїas (SN 864 861)

The criteria for the list this summit relocation affects are:

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height with 30m minimum drop, the list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

The name the hill is listed by is Gїas and it is adjoined to the Pumlumon group of hills, which are situated in the northern part of Mid and West Wales (Region B, Sub-Region B2), and with its summit immersed in a conifer plantation it is encircled by forest tracks and fire breaks and has the Afon Hafren (River Severn) and a minor road further to its north and the Afon Gwy (River Wye) and the A44 road further to its south, and has the town of Llanidloes towards the east.

When the original 400m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website the summit height of this hill was listed as 475m which was based on the spot height positioned at SN 86375 86182 that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

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

When the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013 the hill appeared under the details given above using the six figure grid reference of SN 863 861.  These details were amended for the Y Pedwarau list appearing on Mapping Mountains with the ten figure summit grid reference of SN 86373 86195 used, with this being taken from details on DoBIH.

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 for Gїas

The summit height produced by LIDAR analysis is 474.7m at SN 86489 86191 and its position in relation to that previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, 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, or when the summit of the hill is in a different field compared to where previously given, or when it is positioned to a different feature such as in a conifer plantation, or when the high point of the hill is placed within a different map contour compared to its previous listed position, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.

Therefore, the summit height produced by LIDAR analysis is 474.7m and is positioned at SN 86489 86191, this position is not given a spot height on contemporary Ordnance Survey maps and is approximately 115 metres eastward from where the previously listed summit is positioned.

The full details for the hill are:

Group:  Pumlumon

Name:  Gїas

 

OS 1:50,000 map:  135, 136

Summit Height:  474.7m (LIDAR)

Summit Grid Reference (New Position):  SN 86489 86191 (LIDAR)

Bwlch Height: 435.15m (LIDAR) 

Bwlch Grid Reference:  SN 85917 85246 (LIDAR)

         

Drop:  39.6m (LIDAR)

Myrddyn Phillips and Aled Williams (January 2020)