Saturday, 10 March 2018

Mapping Mountains – Significant Height Revisions – Tumps

Seager Hill South Top (SO 624 379)

There has been a Significant Height Revision when compared to data on contemporary Ordnance Survey 1:25,000 Explorer maps to a hill whose highest summit has been under debate for a number of years, and although the lower of the two summits is not currently classified within any listing to English hills, the higher summit is listed, with one of its classifications being a Tump.  This height revision was initiated be a survey with the Trimble GeoXH 6000 which took place on the 30th January 2018 in good conditions with clear visibility.

The name of the hill is Seager Hill South Top and it is situated in Region 38 the Welsh Borders and in Section 38B West Gloucestershire, Hereford and Worcester.  The hill is positioned with the A 438 road to its north-east and has a number of narrow lanes to its north north-east, east and south, and has the small community of Woolhope Cockshoot to its south-east and Putley towards its east.

As the summit of the hill is not a part of designated open access land permission to visit should be sought, for those wishing to do so a track designated a bridleway ascends to a large barn to the north of the summit with a public footpath then heading north to crest the ridge between this hill and its north-western counterpart, the continuation of this public footpath can also be ascended from the south through a wood, it is only a short walk from where this footpath crests the ridge to the high point of this hill.

Prior to the survey with the Trimble GeoXH 6000 this hill was noted with a 270m summit height based on an 886ft (270.1m) levelled height that appears on the series of Ordnance Survey Six-Inch maps.

Extract from the series of Ordnance Survey Six-Inch maps

The 271.5m (converted to OSGM15) summit height produced by the Trimble GeoXH 6000 is not a dramatic increase from this hill’s current noted height, and in itself does not come within the parameters used within this page heading, however these parameters prioritise numerical data from Ordnance Survey 1:25,000 Explorer maps, and because of this it does come within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any hill whose Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR.  As heights on different scaled Ordnance Survey maps are not consistent the height given on the 1:25,000 Explorer map is being prioritised in favour of the 1:50,000 Landranger map for detailing these revisions.

Extract from the Ordnance Survey 1:25,000 Explorer map

Therefore, this hill’s new summit height is 271.5m (converted to OSGM15) which is 2.5m higher than the 269m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Cardinal Hill:  Seager Hill

Summit Height (New Height):  271.5m (converted to OSGM15)

Name:  Seager Hill South Top

OS 1:50,000 map:  149

Summit Grid Reference:  SO 62418 37928
Drop:  21m

Gathering data with the Trimble GeoXH 6000 at the summit of Seager Hill South Top which resulted in this hill's significant height revision

Myrddyn Phillips (March 2018)

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