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

 

Llanfilo Camp (SO 113 327) 

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 Llanfilo Camp (SO 113 327)

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 name the hill is now listed by is Llanfilo Camp and this was derived from information supplied by Coflein, and it is adjoined to the Mynydd Epynt group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads, with the A38 road farther to its north and the B4560 road farther to its east, and has the town of Talgarth towards the east north-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 310m summit height adjoined to a triangulation pillar positioned at SO 11359 32761 that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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

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 Llanfilo Camp (SO 113 327)

The summit height produced by LIDAR analysis is 310.4m and is positioned at SO 11352 32709, and as this position has no 310m contour on contemporary Ordnance Survey maps 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 310.4m and this was derived from LIDAR analysis, this is 0.4m higher than the previously listed summit height of 310m, which was based on the triangulation pillar positioned at SO 11359 32761.  But as no 310m contour appears at the new summit position it is 10.4m higher than the uppermost 300m contour. 

 

The full details for the hill are: 

Group:  Mynydd Epynt 

Name:  Llanfilo Camp 

OS 1:50,000 map:  161

Summit Height (New Height):  310.4m (LIDAR)                                                           

Summit Grid Reference:  SO 11352 32709 (LIDAR) 

Bwlch Height:  223.6m (LIDAR) 

Bwlch Grid Reference:  SO 09879 31998 (LIDAR) 

Drop:  86.8m (LIDAR) 

 

Myrddyn Phillips (April 2024)