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

Foel Ispri (SH 702 201) – Sub-Trichant addition

There has been confirmation of 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 and LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR summit image of Foel Ispri (SH 702 201)

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. 

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

The name the hill is listed by is Foel Ispri, and it is adjoined to the Y Llethr group of hills, which are situated in the western part of North Wales (Region A, Sub-Region A2), and it is positioned with minor roads to its west and east, the A496 road to its south and the A470 road farther to its east, and has the village of Llanelltyd towards the east south-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 22m of drop, based on the 328m 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 306m based on interpolation of 10m contouring between 300m – 310m. 

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

Since the 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. 

The details for this hill were re-evaluated when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on other publicly available maps and for this hill it had a 327m summit spot height, resulting in the drop value being amended to an estimated c 21m. 

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

Therefore, the confirmation of the addition of this hill to Sub-Trichant status is due to detail on contemporary maps produced from Ordnance Survey data and LIDAR analysis, resulting in a 327.4m summit height and an estimated c 306m 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:  Y Llethr 

Name:  Foel Ispri 

OS 1:50,000 map:  124

Summit Height:  327.4m (LIDAR)                                                           

Summit Grid Reference:  SH 70244 20174 (LIDAR) 

Bwlch Height:  c 306m (interpolation) 

Bwlch Grid Reference:  SH 70216 20385 (interpolation) 

Drop:  c 21m (LIDAR summit and interpolated bwlch) 

 

Myrddyn Phillips (January 2022)