Mapping Mountains – Hill Reclassifications – Y Pellennig – The Remotest Hills of Wales

Llethr Gwaered (SN 795 626) – Pellennig addition 

There has been an addition to the listing of Y Pellennig – The Remotest 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 Llethr Gwaered (SN 795 626)

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

Y Pellennig – The Remotest Hills of Wales - Welsh hills whose summit is at least 2.5km from the nearest paved public road and the hill has 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available as a downloadable e-booklet and print-booklet version on Mapping Mountains Publications with the up-to-date master list available to download on the Mapping Mountains site in Google Doc format.

Y Pellennig - The Remotest Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Llethr Gwaered, and it is adjoined to the Drygarn Fawr group of hills, which are situated in the northern part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north-west, and has the village of Pontrhydfendigaid towards the north-west.

When the original list that later became known as the Y Pellennig – The Remotest Hills of Wales was first compiled, this hill was not included with subsequent documentation giving it an estimated c 13m of drop, based on an estimated c 488m summit height based on interpolation of its uppermost 480m ring contour, and the 475m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

Since the original compilation of this list there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites.

One of the mapping resources now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available maps and has a 489m summit spot height for this hill, and when coupled with the aforementioned 475m bwlch spot height, these values would give this hill 14m of drop. 

Extract from the interactive mapping hosted on the WalkLakes website

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.

Therefore, the addition of this hill to Pellenig status is due to LIDAR analysis, resulting in a 489.5m summit height and a 468.3m bwlch height, with these values giving this hill 21.2m of drop, which is insufficient for it to be classified as a Pellennig. 

The two Llethr Gwaered Pellennig summits; SH 795 626 and SN 801 625

Although this hill was originally unclassified, its adjacent 490m map heighted summit positioned at SN 801 625 was given Pellennig status.  As LIDAR gives this hill as 0.1m lower with 15.0m of drop compared to the summit of the hill positioned at SN 795 626, their respective bylchau are swapped and where there was just one listed Pellennig there are now two Pellennig hills. 

 

The full details for the hill are: 

Group:  Drygarn Fawr

Name:  Llethr Gwaered

OS 1:50,000 map:  147

Summit Height:  489.5m (LIDAR)

Summit Grid Reference:  SN 79564 62624 (LIDAR)

Bwlch Height:  468.3m (LIDAR)

Bwlch Grid Reference:  SN 79609 63025 (LIDAR)   

Drop:  21.2m (LIDAR) 

Remoteness:  3.800km (LIDAR)

 

For the additions and deletions to Y Pellennig – The Remotest Hills of Wales reported on Mapping Mountains please consult the following Change Register:

 

Y Pellennig – The Remotest Hills of Wales

 

Aled Williams and Myrddyn Phillips (May 2026)