Mapping Mountains – Hill Reclassifications – 200m Twmpau

Banc Pontfaen (SN 564 484) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been confirmation of a reclassification to the list of 200m Twmpau, 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 Banc Pontfaen (SN 564 484)

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

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Banc Pontfaen and this was derived from the Ordnance Survey Draft Surveyors Map, and it is adjoined to the Mynydd Bach group of hills, which are situated in the western part of South Wales (Region B, Sub-Region B1), and it is positioned with the A482 road to its north-east, and a minor road to its south-west and east, and has the town of Llanbedr Pont Steffan (Lampeter) towards the east south-east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, the qualifying hill was included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for the main P30 category and listed with a 224m summit height positioned at SN 550 487. 

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

When the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and its summit relocated to SN 564 484 and listed with an estimated c 32m of drop, based on an estimated c 226m summit height and an estimated c 194m bwlch height, with both heights based on interpolation of 5m contouring that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage 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.

Therefore, the confirmation of the reclassification of this hill from 200m Sub-Twmpau status is due to LIDAR analysis, resulting in a 225.6m summit height and a 194.2m bwlch height, with these values giving this hill 31.4m of drop, which is sufficient for it to be classified as a 200m Twmpau. 

 

The full details for the hill are: 

Group:  Mynydd Bach 

Name:  Banc Pontfaen 

OS 1:50,000 map:  146

Summit Height:  225.6m (LIDAR) 

Summit Grid Reference:  SN 56441 48477 (LIDAR) 

Bwlch Height:  194.2m (LIDAR) 

Bwlch Grid Reference:  SN 55294 49452 (LIDAR) 

Drop:  31.4m (LIDAR) 

 

Myrddyn Phillips (December 2022)