Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

Pt. 329.7m (SN 591 630) 

There has been a Significant Height Revision to a hill that is listed in the 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 LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pt. 329.7m (SN 591 630)

The criteria for the list that this height revision 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 hill is being listed by the point (Pt. 329.7m) notation and it is adjoined to the Mynydd Bach group of hills, which are situated in the western part of South Wales (Region B, Sub-Region B1), and it is positioned with the B4576 road to its north-west, B4577 road to its south and a minor road to its east, and has the village of Llangeitho towards the 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. 

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

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 20m of drop, based on an estimated c 327m summit height and an estimated c 307m bwlch height, with both heights based on interpolation of 5m contouring that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage 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 and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites. 

Extract from the interactive mapping hosted on the Magic Maps website

One of the mapping resources now available online is on the Magic Maps website which hosts an interactive map originated from Ordnance Survey data.  Until recently this mapping had many spot heights not on other publicly available maps and for this hill it had a 327m spot height positioned on the summit area of this hill at SN 59019 63010, resulting in its details being amended accordingly.

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 Pt. 329.7m (SN 591 630)

The summit height produced by LIDAR analysis is 329.7m and is positioned at SN 59108 63024, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 329.7m and this was derived from LIDAR analysis, this is 2.7m higher than the previously listed summit height of 327m, which was based on the spot height that appeared on the interactive mapping hosted on the Magic Maps website. 

 

The full details for the hill are: 

Group:  Mynydd Bach 

Name:  Pt. 329.7m 

OS 1:50,000 map:  146

Summit Height (New Height):  329.7m (LIDAR)                                                           

Summit Grid Reference:  SN 59108 63024 (LIDAR) 

Bwlch Height:  306.9m (LIDAR) 

Bwlch Grid Reference:  SN 59361 63409 & SN 59359 63413 (LIDAR) 

Drop:  22.8m (LIDAR) 

 

Myrddyn Phillips (December 2023)