Mapping Mountains – Hill Reclassifications – 30-99m Twmpau

 

Dinas (SH 222 794) – 30-99m Sub-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 Dinas 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 positioned on a promontory with the coast to its west, south and east and has a minor road to its north, and the village of Trearddur towards the east. 

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 Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

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 22m of drop based on an estimated c 30m summit height and an estimated c 8m bwlch height, with both heights based on interpolation of 5m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

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 30m spot height is given on the area of its summit and this is being prioritised in favour of the interpolated summit height with the bwlch height also amended to an estimated c 7m. 

Extract from the Magic Maps website

Therefore, the addition of this hill to 30-99m Sub-Twmpau status is due to detail on contemporary maps produced from Ordnance Survey data, resulting in a 30m summit height and an estimated c 7m bwlch height, with these values giving this hill an estimated c 23m of drop, which is sufficient for it to be classified as a 30-99m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Ynys Môn 

Name:  Dinas 

OS 1:50,000 map:  114

Summit Height:  30m (spot height) 

Summit Grid Reference:  SH 22280 79406 (spot height) 

Bwlch Height:  c 7m (interpolation) 

Bwlch Grid Reference:  SH 22248 79489 (interpolation) 

Drop:  c 23m (spot height summit and interpolated bwlch) 

 

Myrddyn Phillips (April 2021)