Saturday, 8 February 2020

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

Mynydd Dir (SH 915 712) – Sub-Trichant reclassified to Trichant

There has been confirmation of a reclassification 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 Ordnance Survey maps.

The criteria for the list that this reclassification 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 13th May 2017.

The name the hill is listed by is Mynydd Dir, and it is adjoined to the Rhos group of hills which are situated in the northern part of North Wales (Region A, Sub-Region A2), and it is positioned with the B4381 road to its north and the A548 road to its south and east, and has the village of Llanfair Talhaiarn towards the south-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s website this hill was included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for the main P30 list. 

When 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 30m of drop, based on the 314m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and an estimated bwlch height of c 284m based on interpolation of 10m contouring between 280m – 290m.

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

The details for this hill were re-assessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available Ordnance Survey maps and also for this area it had contour intervals at 5m.  Therefore, the drop value was amended to an estimated c 32m based on interpolation of bwlch contouring between 280m – 285m.

The details for this hill were also re-assessed when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and used to appear on the online Vector Map Local.  This latest re-assessment resulted in the hill being listed with an estimated c 36m of drop, based on interpolation of 5m bwlch contouring between 275m – 280m.

Extract from the OS Maps website

Therefore, the confirmation of the reclassification of this hill from Sub-Trichant status is due to detail on contemporary Ordnance Survey maps, resulting in a 314m summit height and an estimated c 278m bwlch height, with these values giving this hill c 36m of drop, which is sufficient for it to be classified as a Trichant.

The full details for the hill are:

Group:  Rhos

Name:  Mynydd Dir

OS 1:50,000 map:  116

Summit Height:  314m (spot height)

Summit Grid Reference:  SH 91597 71238 (hand-held GPS via DoBIH)

Bwlch Height:  c 278m (interpolation)

Bwlch Grid Reference:  SH 91337 71524 (interpolation)

Drop:  c 36m (spot height summit and interpolated bwlch)

Myrddyn Phillips (February 2020)

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