Thursday, 20 August 2015

Mapping Mountains – Significant Height Revisions – Y Pedwarau

Craig y Ganllwyd (SH 707 258)

There has been a Significant Height Revision to the listing of the Y Pedwarau initiated from a survey with the Trimble GeoXH 6000, with these details being retrospective as the survey that resulted in this height revision was conducted on 3rd May 2014.  With the criteria for Pedwar inclusion being all Welsh hills at or above 400m and below 500m in height that have a minimum of 30m of drop.

The name of the hill is Craig y Ganllwyd and it is situated in the hills of the Rhinogydd, which are positioned in the west of North Wales between Abermaw (Barmouth) in the south and Trawsfynydd in the north.

Prior to the survey with the Trimble GeoXH 6000 the hill was listed as a 400m Sub-Pedwar and through this survey it has been reclassified to a Pedwar, and it can be accessed from the small community of Ganllwyd to its south-east.  However, even though forest paths and tracks head toward the hill much of the land outside of these is rough and wild.  This should not put you off though, as when this hill is combined with its neighbours of Craig Aberserw and Craig y Derlwyn they make one of the better outings in the eastern part of the Rhinogydd.

The summit height of this hill has been dramatically increased from its current Ordnance Survey 1:25,000 Explorer map height, the detail on the 1:25,000 map does not have a spot height and its uppermost contour ring is 410m, whilst Harvey Maps has a 423m spot height for this hill, which was relied upon when the hill was listed as a 400m Sub-Pedwar.  To confuse matters the Ordnance Survey 1:50,000 Landranger map has an uppermost 430m contour ring which compliments detail on the 1:2,500 base map which has an imperial height of 1,411ft (430m).

Although the new summit height of 430.9m (converted to OSGM15) is similar to the Ordnance Survey 1:50,000 and 1:2,500 map detail, the 1:25,000 map is being prioritised for this page heading where the summit height is not consistent between the different scales of paper mapping that the Ordnance Survey produce.  Therefore this hill’s new summit height is 7.9m higher than its previously listed height which came from the 423m Harvey Maps spot height, and it is a dramatic 20.9m higher than the uppermost 410m ring contour on current Ordnance Survey 1:25,000 Explorer maps.

The full details for the hill are:

Cardinal Hill:  Y Llethr

Summit Height (New Height):  430.9m (converted to OSGM15)

Name:  Craig y Ganllwyd

OS 1:50,000 map:  124

Summit Grid Reference:  SH 70775 25853
Drop:  33.4m (converted to OSGM15)

Gathering data from the summit of Craig y Ganllwyd which resulted in this hill's significant height revision

Myrddyn Phillips and Aled Williams (August 2015)

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