Sunday, 25 June 2017

Mapping Mountains – Hill Reclassifications – 200m Twmpau

Pen y Gaer (SO 139 976) – 200m Twmpau reclassified to Trichant


There has been a reclassification of a 200m Twmpau (thirty welsh metre prominences and upward) to the listing of Y Trichant due to surveying with the Trimble GeoXH 6000.

The details relating to this hill’s inclusion in the listing of Y Trichant are retrospective as the survey with the Trimble took place on the 11th January 2015 and the Hill Reclassifications post for its 300m Twmpau status was published on Mapping Mountains on the 12th January 2015.

The criteria for 200m Twmpau status is all Welsh hills at or above 200m and below 300m in height with 30m minimum drop, whilst Y Trichant is the title for the hills in the 300m height band of the Twmpau and takes in all Welsh hills at or above 300m and below 400m in height with 30m minimum drop, with the introduction to the re-naming of this list appearing on Mapping Mountains on the 13th May 2017.

Prior to the survey with the Trimble GeoXH 6000 the hill was listed with 87m of drop based on the 299m summit spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and the 212m bwlch spot height that appears on the Ordnance Survey enlarged mapping hosted on the Geograph website.

The hill is situated in the Carnedd Wen range with its Cardinal Hill being Stingwern Hill (SJ 132 014) and is placed in the North Wales Region (Region A, Sub-Region A4), and is positioned with the small community of Bettws Cedewain to the west south-west and Aber-miwl (Abermule) to the south-east.

As the summit of the hill is not a part of designated open access land permission to visit its high point should be sought.  For those seeking this and wishing to visit there is a public footpath just to the north of the summit which can be accessed from either the north-east or the south-west.

The name of the hill is Pen y Gaer and it is only the third hill that I know of whose status has been altered due to the Ordnance Survey remodelling known as OSGM15.  This remodelling has increased the accurately known height of hills in Wales by approximately 2-4cm, and the other two hills whose status was altered because of OSGM15 are Calf Top (SD 664 856) and Carn Ysgubor (SM 699 246).


Surveyed height of Pen y Gaer pre OSGM15 = 299.974m

Surveyed height of Pen y Gaer post OSGM15 = 300.002m



The full details for the hill are:

Cardinal Hill:  Stingwern Hill

Summit Height:  300.0m (converted to OSGM15)

Name:  Pen y Gaer

OS 1:50,000 map:  136

Summit Grid Reference:  SO 13997 97677

Drop:  88m



Pen y Gaer (SO 139 976) reclassified from a 200m Twmpau to a Trichant



Myrddyn Phillips (June 2017)









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