Mapping Mountains – Significant Height Revisions – 200m Twmpau

 

Cae Pen Crug (SN 654 592) 

There has been a Significant Height Revision to a hill that is listed in the 200m Twmpau, 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 Cae Pen Crug (SN 654 592)

The criteria for the list that this height revision applies to are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

The 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cae Pen Crug and this was derived from the Tithe map, 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 a minor road to its north, the B4578 road to its west, the B4342 road to its south and the A485 road to its east, and has the town of Tregaron towards the east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a summit height of 224m based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and which is positioned at SN 655 590. 

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 Cae Pen Crug (SN 654 592)

The height produced by LIDAR analysis to the summit of this hill is 229.1m positioned at SN 65493 59251, and this height 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 229.1m and this was derived from LIDAR analysis, this is 5.1m higher than the previously listed summit height of 224m, which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Mynydd Bach 

Name:  Cae Pen Crug 

OS 1:50,000 map:  146

Summit Height (New Height):  229.1m (LIDAR) 

Summit Grid Reference:  SN 65493 59251 (LIDAR) 

Bwlch Height:  194.2m (LIDAR) 

Bwlch Grid Reference:  SN 65231 59601 (LIDAR) 

Drop:  34.9m (LIDAR) 

 

Myrddyn Phillips (October 2022)