Thursday, 27 August 2015

Mapping Mountains – Significant Height Revisions – Yr Uchafion and 700m Twmpau

Llechog (SH 606 567) 

There has been a Significant Height Revision initiated by a survey with the Trimble GeoXH 6000, with this hill being listed in both the Yr Uchafion and the 700m Twmpau (thirty welsh metre prominences and upward), with these details being retrospective as the survey that resulted in this height revision was conducted on 9th September 2014.

The criteria for these listings appear below:

Yr Uchafion - All Welsh hills at or above 500m in height that have 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams

700m Twmpau - All Welsh hills at or above 700m and below 800m in height with 30m minimum drop.  With the 700m Sub-Twmpau being all Welsh hills at or above 700m and below 800m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips.   

The name of the hill is Llechog and it is situated in the hills adjoined to the Yr Wyddfa range which is positioned in the heartland of Eryri, and the survey was conducted on a beautiful sunny September day.

The hill can be accessed from the Llanberis Path which is one of the six main paths up Yr Wyddfa.  This path roughly follows the course of the railway line as it ascends the mountain from Llanberis, with Llechog standing on a ridge that is seldom visited by the multitude of walkers who head toward the summit of Wales’ highest mountain.

The height given the hill on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps is 718m, with the height resulting from the survey with the Trimble GeoXH 6000 being 720.0m (converted to OSGM15).  This is not a dramatic height revision 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 height 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.

Therefore this hill’s new summit height is 2.0m higher than its previously listed height which came from the 718m spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

The full details for the hill are:

Cardinal Hill:  Yr Wyddfa

Summit Height (New Height):  720.0m (converted to OSGM15)

Name:  Llechog

OS 1:50,000 map:  115

Summit Grid Reference:  SH 60613 56751
Drop:  28.0m (converted to OSGM15)

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

Myrddyn Phillips and Aled Williams (August 2015)

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