Mapping Mountains – Hill Reclassifications – Y Trichant – The 300m Hills of Wales

Y Grug (SH 809 103) – Sub-Trichant addition

There has been an addition to the list of Y Trichant – The 300m Hills of Wales, 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: 

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Y Grug, and it is adjoined to the Aran Fawddwy group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with the A470 road to its east and north, the A487 road to its west and a minor road to its north, and has the small town of Dinas Mawddwy towards the north-east. 

When the original 300m 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 18m of drop, based on the 376m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 358m bwlch spot height positioned at SH 80775 10135 that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

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

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of 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 were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current such as the interactive mapping on the Magic Maps and WalkLakes websites. 

One of the resources recently available online is the mapping on the OS Maps website and the details for this hill were subsequently re-assessed against this mapping.  This is the replacement for OS Get-a-map and until recent times had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000 Explorer map and used to appear on the online Vector Map Local.  This mapping had bwlch contouring between 355m – 360m; with interpolation placing the height of the bwlch as an estimated c 356m and this position is favoured over that of the 358m spot height. 

Therefore, the addition of this hill to Sub-Trichant status is due to detail on contemporary maps produced from Ordnance Survey data, resulting in a 376m summit height and an estimated c 356m bwlch height, with these values giving this hill an estimated c 20m of drop, which is sufficient for it to be classified as a Sub-Trichant. 

 

The full details for the hill are: 

Group:  Aran Fawddwy 

Name:  Y Grug 

OS 1:50,000 map:  124, 125

Summit Height:  376m (spot height)                                                           

Summit Grid Reference:  SH 80961 10323 (spot height) 

Bwlch Height:  c 356m (interpolation) 

Bwlch Grid Reference:  SH 80813 10183 (interpolation) 

Drop:  c 20m (spot height summit and interpolated bwlch) 

 

Myrddyn Phillips (January 2022)