Mapping Mountains – Summit Relocations – Y Trichant and Y Trechol – The Dominant Hills of Wales

Mynydd y Lan (ST 209 923)

There has been a Summit Relocation to a hill that is listed in the Y Trichant and Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Mynydd y Lan (ST 209 923)

The criteria for the two listings that this summit relocation applies to are:

Y Trichant – Welsh hills at or above 300m and below 400m in height with 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 Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015.

The name of the hill is Mynydd y Lan and it is adjoined to the Cymoedd Gwent group of hills, which are situated in the eastern part of South Wales (Region C, Sub-Region C2), and it is encircled by roads with the B4251 to its south and west, the A472 to its north and the A467 and B4591 and the Afon Ebwy (Ebbw River) to its east, and has the town of Trecelyn (Newbridge) towards the north and the village of Pontycymer (Crosskeys) towards the east.

When the original Welsh 300m P30 list was published on Geoff Crowder’s v-g.me website this hill was listed with a 381m summit height, based on the spot height positioned at ST 20794 92508 that appears on the Ordnance Survey 1:25,000 Explorer map, with an accompanying note stating that the Ordnance Survey 1:50,000 Landranger map has a 385m spot height positioned at ST 20898 92357.  As heights on 1:25,000 scale mapping were prioritised in this list over those on 1:50,000 scale mapping this hill’s summit was listed to where the 381m spot height appears on the 1:25,000 Explorer map.

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

Extract from the Ordnance Survey 1:50,000 Landranger map

Since publication of these P30 lists on Geoff Crowder’s v-g.me website 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 Vector Map Local hosted on the Geograph website, and which is entitled the Interactive Coverage Map, and in the case of this hill it is the series of Ordnance Survey Six-Inch maps where the origins of the 385m spot height that appears on the 1:50,000 Landranger map can be traced, as the Six-Inch map surveyed in 1875 and published in 1885 has a 1263.6ft (385.15m) surface height at the same position as the contemporary 385m spot height.

Extract from the Ordnance Survey series of Six-Inch maps

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.

LIDAR summit image of Mynydd y Lan

The summit height produced by LIDAR analysis and its position in relation to that previously given comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to any listed hill whose summit meets the following criteria; where there are a number of potential summit positions within close proximity and the highest point is not where previously given, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist, or when the summit of the hill is in a different field compared to where previously given, or when the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary that is judged to be a relatively recent man-made construct.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these relocations.

The summit height produced by LIDAR analysis is 381.3m and is positioned at ST 20903 92337, this position is given a 385m spot height on contemporary Ordnance Survey 1:50,000 Landranger maps and is approximately 200 metres south south-eastward from the previously listed summit position where the 381m spot height appears on the Ordnance Survey 1:25,000 Explorer map.  

The full details for the hill are:

Group:  Cymoedd Gwent

Name:  Mynydd y Lan

OS 1:50,000 map:  171

Summit Height:  381.3m (LIDAR)

Summit Grid Reference (new position):  ST 20903 92337 (LIDAR)

Bwlch Height:  159.5m (LIDAR)

Bwlch Grid Reference:  ST 19806 96725 (LIDAR)

Drop:  221.8m (LIDAR)

Dominance:  58.17% (LIDAR)

Myrddyn Phillips (July 2019)