Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

 

Clegyrog Ganol (SH 385 894) – 30-99m Twmpau addition

There has been an addition to the list of 30-99m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data. 

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

30-99m Twmpau – Welsh hills at or above 30m and below 100m in height that have 30m minimum drop, with an accompanying sub list entitled the 30-99m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 30m and below 100m 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 30-99m Twmpau by Myrddyn Phillips

The name the hill is listed by is Clegyrog Ganol and this was derived from the Tithe map, and it is adjoined to the Ynys Môn group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A1), and it is encircled by minor roads with the A5025 road farther to the north-west and the B5111 road farther to the east, and has the village of Llanfechell towards the north-west. 

When the original 30-99m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the main P30 or the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for either 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-evaluated and it was listed with an estimated c 31m of drop based on the 99m summit 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, and an estimated c 68m bwlch height based on interpolation of 5m contouring between 65m – 70m that appears on the Ordnance Survey 1:25,000 Explorer map. 

Therefore, the addition of this hill to 30-99m Twmpau status is due to detail on contemporary maps produced from Ordnance Survey data, resulting in a 99m summit height and an estimated c 68m bwlch height, with these values giving this hill an estimated c 31m of drop which is sufficient for it to be classified as a 30-99m Twmpau.

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Clegyrog Ganol 

OS 1:50,000 map:  114

Summit Height:  99m (spot height) 

Summit Grid Reference:  SH 38569 89439 (hand-held GPS via DoBIH) 

Bwlch Height:  c 68m (interpolation) 

Bwlch Grid Reference:  SH 40950 89190 (interpolation) 

Drop:  c 31m (spot height summit and interpolated bwlch) 

 

Myrddyn Phillips (March 2021)