Thursday, 4 August 2016

Mapping Mountains – Significant Height Revisions – Y Pedwarau


Clip yr Orsedd (SH 711 747) 

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000 to a hill that is listed in the Y Pedwarau, with the survey that resulted in this height revision being conducted on 14th July 2016.  The criteria for Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 30m minimum drop.

The name of the hill is Clip yr Orsedd and it is situated in the northern part of the Carneddau range of hills which is in north-west Wales.  This hill range comprises some of the highest mountains in the country but the evening walk when the survey was conducted concentrated on some of its lower hills.

The hill is positioned above the towns of Llanfaifechan which is to its west and Penmaenmawr which is to its north north-east and it can be easily accessed from a green track that continues from the end of a minor lane to the hill’s west.  An alternative route is via part of the Wales Coast Path, with both routes just bi-passing the summit to its south.

Prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 429m, with this height taken from the Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey enlarged mapping hosted on the Geograph website.

The summit of Clip yr Orsedd was surveyed with the Trimble GeoXH 6000 as being 426.6m (converted to OSGM15).  This is not a dramatic height revision when compared to some revised heights, but it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revision applies to any listed hill whose Ordnance Survey summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 map is being prioritised for detailing these revisions.

The summit of this hill is easily identified and consists of an outcrop of rock close to the ground and therefore this hill’s new summit height as surveyed by the Trimble GeoXH 6000 is 426.6m (converted to OSGM15) which is 2.4m lower than its previously listed height of 429m which appears on the Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey enlarged mapping hosted on the Geograph website.


The full details for the hill are:

Cardinal Hill:  Tal y Fan

Summit Height:  426.6m (converted to OSGM15)

Name:  Clip yr Orsedd

OS 1:50,000 map:  115

Summit Grid Reference:  SH 71185 74743

Drop:  39.5m (converted to OSGM15)


The Trimble GeoXH 6000 gathering data at the summit of Clip yr Orsedd (SH 711 747) which resulted in this hill's significant height revision


Myrddyn Phillips and Aled Williams (August 2016)





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