Mapping Mountains – Significant Height Revisions – 200m Twmpau

 

Pt. 275.1m (SO 131 995)

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 confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Pt. 275.1m (SO 131 995)

The criteria for the list this height revision affects 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 hill is being listed by the point (Pt. 275.1m) notation as an appropriate name for it either through local enquiry and / or historic research has not been found by the author, and it is adjoined to the Carnedd Wen group of hills which are situated in the south-eastern part of North Wales (Region A, Sub-Region A4), and it is encircled by minor roads, with the B4390 road to its north, the B4389 road to its west and the A483 road further to its south-east, and has the village of Tregynon towards the west south-west. 

When the original 200m 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 summit height of 273m, which was taken from the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

The summit height produced by the Trimble GeoXH 6000 survey is 275.1m, this is not a dramatic height revision when compared to some survey results, but it does come 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 summit 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. 

The Trimble GeoXH 6000 gathering data at the summit of Pt. 275.1m (SO 131 995)

Therefore, this hill’s new listed summit as surveyed with the Trimble GeoXH 6000 is 275.1m, this is positioned at SO 13195 99523 and is 2.1m higher than its previously listed height of 273m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

 

The full details for the hill are:

Group:  Carnedd Wen

Name:  Pt. 275.1m

OS 1:50,000 map:  136

Summit Height (new height):  275.1m (converted to OSGM15)

Summit Grid Reference:  SO 13195 99523 

Bwlch Height:  241.3m (converted to OSGM15)

Bwlch Grid Reference:  SO 12737 99457

Drop:  33.8m

 

Myrddyn Phillips (January 2021)