Twyn Crug yr Afan (SS 920 954)
There has been a Significant Height Revision to a hill that is listed in the 500m Twmpau and The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams.
Twyn Crug yr Afan (SS 920 954) |
500m Twmpau – Welsh hills at or above
500m and below 600m in height that have 30m minimum drop, with an accompanying
sub category entitled the 500m Sub-Twmpau consisting of all Welsh hills at or
above 500m and below 600m in height that have 20m or more and below 30m of drop. With the word Twmpau being an acronym
standing for thirty welsh metre prominences and upward. The list is authored by Myrddyn Phillips and is published on Mapping Mountains in Google Doc format.
The 500m Twmpau by Myrddyn Phillips |
The Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams |
Extract from the Ordnance Survey 1:50,000 Landranger map |
Extract from the Ordnance Survey 1:25,000 Explorer map |
The details for this hill were reassessed when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online. This mapping had many spot heights not on other publicly available maps and for this hill it had a 559m summit spot height adjoined to the ancient tumulus and positioned at SS 92037 95445.
One of the mapping resources now available online is the Magic Maps website which hosts an interactive map originated from Ordnance Survey data. This mapping also has many spot heights not on other publicly available Ordnance Survey maps and for this hill the 559m summit spot height is also shown.
Extract from the Magic Maps website |
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.
The Trimble GeoXH 6000 gathering data at the summit of Twyn Crug yr Afan |
The full details for the hill are:
Group: Cymoedd Morgannwg
Name: Twyn Crug yr
Afan
OS 1:50,000 map: 170
Summit Height (New Height):
560.2m (converted to OSGM15)
Summit Grid Reference:
SS 92035 95448
Bwlch Height: 526.0m (converted
to OSGM15)
Bwlch Grid Reference:
SS 92019 95054
Drop: 34.2m
Aled Williams and Myrddyn Phillips (August 2021)
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