Saturday, 25 April 2015

Mapping Mountains – Hill Reclassifications – Y Pellennig – The Remotest Hills of Wales

Pen Diban (SH 112 205) - Pellennig addition

There has been a re-instatement of a Pellennig hill due to a recent Trimble survey.  The hill is situated on Ynys Enlli and is positioned at the south of the island; its name is Pen Diban.

Pen Diban (SH 112 205) was included in the original list of Y Pellennig that was published on Geoff Crowder’s website and listed with a 20m high summit and a c 5m high bwlch, giving a drop of c 15m.  The drop was estimated and based on contour interpolation with the Ordnance Survey 1:25,000 paper maps having 10m contour intervals.
Since the original publication of Y Pellennig, the Ordnance Survey enlarged mapping on the Geograph website has become available; this mapping for the area where Pen Diban is situated gives contour intervals at 5m and narrows the area and the height of the bwlch to c 5m – c 10m.  Therefore the drop of Pen Diban was re-evaluated as c 14m and it was deleted from the ranks of Y Pellennig – The Remotest Hills of Wales.

This hill has now been surveyed with the Trimble GeoXH 6000, its surveyed summit height is 20.0m (converted to OSGM15) and its surveyed bwlch height is 5.0m (converted to OSGM15).

The raw processed survey result for the summit is 19.975m converted to OSGM15

The raw processed survey result for the bwlch is 4.982m converted to OSGM15

The margin of uncertainty for the height in relation to the position of the Trimble on the summit is 0.0m and for the bwlch 0.05m.

The precision of the equipment is +/- 0.15m.

The accuracy of the equipment is 0.1m.

Therefore the raw result for the drop should be rounded to one decimal place; 15.0m

This now brings the overall total for Y Pellennig to 167 hills for the Complete list (All Wales), with the total for the Mainland Wales list remaining the same at 124 hills.  The Master List will be duly updated on the Mapping Mountains blog.

The full details for the hill are:

Cardinal Island:  Ynys Enlli

Summit Height:  20.0m (converted to OSGM15)

Name:  Pen Diban

OS 1:50,000 map:  123

Summit Grid Reference:  SH 112 205

Drop:  15.0m (converted to OSGM15)

Pen Diban (SH 112 205) the re-instated Pellennig hill

For details on the survey that promoted this hill to Pellennig status please click {here}

Myrddyn Phillips and Aled Williams (April 2015)

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