Mapping Mountains – Hill Reclassifications – 200m Twmpau

 

Mynydd Cefn Maes Mawr (SN 728 985) – 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 confirmed by LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Mynydd Cefn Maes Mawr (SN 728 985)

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 name the hill is listed by is Mynydd Cefn Maes Mawr and this was derived from the Tithe map, and it is adjoined to the Pumlumon group of hills, which are situated in the north-western part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with the A487 road to its north-west and minor roads to its south and east, and has the town of Machynlleth towards the north-east. 

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for the main P30 category. 

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

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed with 33m of drop, based on the 227m summit spot height and the 194m bwlch spot height that appeared on the Ordnance Survey Vector Map Local that was 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 226.8m summit height and a 193.9m bwlch height, with these values giving this hill 32.85m of drop, which is sufficient for it to be classified as a 200m Twmpau.

 

The full details for the hill are: 

Group:  Pumlumon 

Name:  Mynydd Cefn Maes Mawr 

OS 1:50,000 map:  135

Summit Height:  226.8m (LIDAR) 

Summit Grid Reference:  SN 72878 98500 (LIDAR) 

Bwlch Height:  193.9m (LIDAR) 

Bwlch Grid Reference:  SN 72854 97986 (LIDAR) 

Drop:  32.85m (LIDAR) 

 

Myrddyn Phillips (February 2021)