Thursday, 20 August 2015

Mapping Mountains – Significant Height Revisions – Y Pedwarau


Craig y Ganllwyd (SH 707 258)

This is the seventh post under the heading of Significant Height Revisions, and the following details are retrospective as the Trimble survey that resulted in this height revision was conducted on 3rd May 2014.

The seventh major height revision initiated from a survey with the Trimble GeoXH 6000 was conducted in the hills of the Rhinogydd, which are situated in the west of North Wales between Abermaw (Barmouth) in the south and Trawsfynydd in the north.

The hill was reclassified as a Pedwar after this survey and 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 Ganllwyd they make one of the better outings in the eastern part of the Rhinogydd.

The name of the hill is Craig y Ganllwyd and its summit height has been dramatically increased from its current Ordnance Survey 1:25,000 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 Aled and I relied on when we listed this hill as a Sub-Pedwar.  To confuse matters even more the Ordnance Survey 1:50,000 map has an uppermost 430m contour ring and the 1:2,500 base map has an imperial height of 1,411ft (430m).

Although the new summit height of 430.9m 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 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 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


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

For details on the survey that significantly revised the summit height of this hill please click {here}

Myrddyn Phillips and Aled Williams (May 2014)



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