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

 

Pigyn Shôn Nicolas (SN 667 354) – 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 Pigyn Shôn Nicolas, and it is adjoined to the Mynydd Mallaen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north, west and south-east, and the B4302 road to its north-west, and has the town of Llanymddyfri (Llandovery) towards the 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 an estimated c 19m of drop, based on the 322m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map at SN 66753 35404 and SN 66689 34767 and an estimated c 303m bwlch height, based on interpolation of 10m contouring between 300m – 310m. 

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

One of the resources recently available online is the mapping on the OS Maps website.  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.  Although the mapping on the OS Maps website no longer has contours at 5m intervals, such contours are represented on other mapping available online and for this hill this mapping has bwlch contouring between 300m – 305m, with interpolation placing the height of the bwlch as an estimated c 301m. 

Interactive map with 5m contouring available online

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 322m summit height and an estimated c 301m bwlch height, with these values giving this hill an estimated c 21m of drop, which is sufficient for it to be classified as a Sub-Trichant. 

 

The full details for the hill are: 

Group:  Mynydd Mallaen 

Name:  Pigyn Shôn Nicolas 

OS 1:50,000 map:  146

Summit Height:  322m (spot height)                                                           

Summit Grid Reference:  SN 66753 35404 & SN 66689 34767 (spot height) 

Bwlch Height:  c 301m (interpolation) 

Bwlch Grid Reference:  SN 67137 35439 (interpolation) 

Drop:  c 21m (spot height summit and interpolated bwlch) 

 

Myrddyn Phillips (June 2023)