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

Pt. 526.8m (SN 745 611) – Pellennig deletion 

There has been a deletion 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 a Trimble GeoXH 6000 summit survey and LIDAR bwlch analysis conducted by Myrddyn Phillips and Aled Williams. 

Pt. 526.8m (SN 745 611)

The criteria for the list that this deletion 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 hill is being listed by the point (Pt. 526.8m) notation and it is adjoined to the Esgair Wen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its north and south, and has the small community of Pontrhydfendigaid towards the north-west and the town of Tregaron towards the 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 as with a 527m summit spot height and bwlch contouring between 510m – 520m that appear on the contemporary Ordnance Survey 1:25,000 Explorer map, interpolation gave this hill less than 15m of drop. 

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 resources recently available online is the mapping on the OS Maps website and the details for this hill were subsequently re-assessed against this mapping.  This is the replacement for OS Get-a-map and until recent times had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000 Explorer map and used to appear on the online Vector Map Local.  This mapping had bwlch contouring between 510m – 515m, with interpolation placing the height of the bwlch as an estimated c 511m, and when coupled with the 527m summit spot height these values gave this hill an estimated c 16m of drop, and therefore it was included as a Pellennig with 2.700km of remoteness. 

Extract from the interactive mapping that was hosted on the OS Maps website

The hill was subsequently surveyed with the Trimble GeoXH 6000, resulting in a 526.8m summit height and a 511.9m bwlch height.  Although this survey gave this hill 14.9m of drop, it was decided that the bwlch position was incorrect and therefore the hill was retained as a Pellennig. 

The Trimble GeoXH 6000 gathering data at the summit of Pt. 526.8m (SN 745 611)

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 image of Pt. 526.8m (SN 745 611)

Therefore, the deletion of this hill from Pellenig status is due to a Trimble GeoXH 6000 summit survey and LIDAR bwlch analysis, resulting in a 526.8m summit height and a 512.0m bwlch height, with these values giving this hill 14.8m of drop, which is insufficient for it to be classified as a Pellennig. 

 

The full details for the hill are: 

Group:  Esgair Wen

Name:  Pt. 526.8m

OS 1:50,000 map:  146, 147

Summit Height:  526.8m (Trimble GeoXH 6000)

Summit Grid Reference:  SN 74595 61119 (Trimble GeoXH 6000)

Bwlch Height:  512.0m (LIDAR)

Bwlch Grid Reference:  SN 74980 61422 (LIDAR)   

Drop:  14.8m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

Remoteness:  2.700km (no longer applicable)

 

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 (November 2023)