Mapping Mountains – Hill Reclassifications – 100m Twmpau

Tŷ Canol (SH 471 907) – 100m Sub-Twmpau addition 

There has been an addition to the list of 100m 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: 

100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau with the criteria for this sub category being all Welsh hills at or above 100m and below 200m 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 100m Twmpau by Myrddyn Phillips

The name the hill is listed by is Tŷ Canol 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 its west, and has the village of Pen-y-sarn towards the west south-west. 

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub 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 21m of drop, based on the 165m summit spot height and the 144m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

Since the original publication of the P30 lists on Geoff Crowder’s v-g.me website and the re-assessment of this hill’s details there have been a number of Ordnance Survey 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 are current and digitally updated such as the mapping on the Magic Maps website. 

Extract from the Magic Maps website

One of the mapping resources now available online is the Magic Maps website which hosts an interactive map originated from Ordnance Survey data.  This map has many spot heights not on other publicly available Ordnance Survey maps and for this hill a 166m spot height is given on the area of its summit and this is being prioritised in favour of the aforementioned 165m spot height. 

Therefore, the addition of this hill to 100m Sub-Twmpau status is due to detail on contemporary maps produced from Ordnance Survey data, resulting in a 166m summit height and a 144m bwlch height, with these values giving this hill 22m of drop which is sufficient for it to be classified as a 100m Sub-Twmpau.

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Tŷ Canol 

OS 1:50,000 map:  114

Summit Height:  166m (spot height) 

Summit Grid Reference:  SH 47141 90737 (spot height) 

Bwlch Height:  144m (spot height) 

Bwlch Grid Reference:  SH 47087 91141 (spot height) 

Drop:  22m (spot height summit and bwlch) 

 

Myrddyn Phillips (March 2021)