Thursday, 4 August 2016

Mapping Mountains – Significant Height Revisions – Y Pedwarau

Clip yr Orsedd (SH 711 747) 

This is the thirty second post under the heading of Significant Height Revisions, and the Trimble survey that resulted in this height revision was conducted on the 14th July 2016 in clear conditions during the evening in the company of Aled Williams.

The thirty second major height revision initiated from a survey with the Trimble GeoXH 6000 was conducted in the northern Carneddau in north-west Wales.  This hill range comprises some of the highest mountains in the country but the evening walk 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.

The name of the hill is Clip yr Orsedd and prior to the survey with the Trimble GeoXH 6000 the height of the hill was listed as 429m.  This height appears on the Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey enlarged map on the Geograph website.

It was surveyed with the Trimble GeoXH as being 426.6m high.  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 surveyed Trimble height, 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 the hill is easily distinguishable 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 enlarged mapping on the Geograph website and the 1:25,000 Explorer map.

The full details for the hill are:

Cardinal Hill:  Carnedd Llywelyn

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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