Mapping Mountains – Summit Relocations – 200m Twmpau

Banc Pontfaen (SN 564 484) 

There has been a Summit Relocation to a hill that is listed in the 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 summit relocation 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 listed with a summit height of 224m based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is 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. 

LIDAR image of Tyn Ffynnon (224.3m at SN 549 487 [on left] and Banc Pontfaen (225.6m at SN 564 484 [on right])

The height produced by LIDAR analysis to the summit of this hill is 225.6m positioned at SN 56441 48477, as opposed to where the 224m spot height appears which LIDAR gives as 224.3m positioned at SN 54956 48738, and this position comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to when the high point is positioned in a different field, to a different feature such as a conifer plantation, within a different map contour, a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit 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.

Therefore, the summit height produced by LIDAR analysis is 225.6m which is positioned at SN 56441 48477, 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 1500 metres eastward from where the previously listed summit is positioned. 

 

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 (New Position):  SN 56441 48477 (LIDAR) 

Bwlch Height:  194.2m (LIDAR) 

Bwlch Grid Reference:  SN 55294 49452 (LIDAR) 

Drop:  31.4m (LIDAR) 

 

Myrddyn Phillips (December 2022)