Mapping Mountains – Significant Height Revisions – The Fours – The 400m Hills of England

Green Side (NT 906 076)

There has been a Significant Height Revision to a hill that is listed in the The Fours – The 400m Hills of England, with the summit height, col height and their locations, the drop and status of the hill confirmed by LIDAR analysis.

This was initiated by Joe Nuttall who produced a summit analysis programme that used LIDAR with an alternative height map (DEM) allowing identification of summits and cols and thereby drops.  The resulting spreadsheet that Joe produced contains over 29600 hills.

This spreadsheet is being evaluated by DoBIH Editors and others, and for this particular hill it was Jim Bloomer who initially assessed its height and that of its adjacent peak via LIDAR analysis.

Myrddyn Phillips then evaluated this hill’s details via LIDAR analysis and confirmed its height revision, summit relocation and addition as a 390m Sub-Four.

LIDAR image of Green Side (NT 906 076)

The criteria for the list this height revision affects are:

The Fours – The 400m Hills of England.  English hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main listing of The Fours are three categories of sub hills, with this hill being added to the 390m Sub-Four category, the criteria for which are all English hills at or above 390m and below 400m in height that have 30m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and the 2nd edition of the booklet containing this list was published by Mapping Mountains Publications on the 24th April 2018.

The Fours - The 400m Hills of England by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Green Side, and it is adjoined to The Cheviot group of hills, which are situated in the north-eastern part of England (Region 33 Scottish Border to the River Tyne), and it is positioned with a minor road to its south-east and farther afield has the A68 road to its south-west, the B6341 road to its south-east and the A697 road to its east, and has the town of Rothbury towards the east south-east.

When the 2nd edition of the The Fours – The 400m Hills of England was published by Mapping Mountains Publications in April 2018, this hill was not classified but was listed with an estimated c 17m of drop, based on the 389m summit height adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and an estimated c 372 col height based on interpolation of 5m contouring between 370m – 375m that appear on the OS Maps website.

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

Approximately 1km to the north-east of the triangulation pillar atop Green Side is the hill named Lord’s Seat.  The flush bracket adjoined to this trig pillar is given as 389.534m and positioned at NT 90299 07313 in the OS Trig Database, with its map height given as 389m.  As the map height of Lord’s Seat is 392m it was this hill that was classified as the 390m Sub-Four with c 53m of drop.

However, it was not until LIDAR became available that the details for these two hills could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

The summit height produced by LIDAR analysis for these two hills is given below:

Lord’s Seat:  392.2m at NT 91281 07968 and NT 91282 07966

Green Side:  395.5m at NT 90695 07602

The above detail comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated summit height and 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 analysis.

LIDAR summit image of Green Side

Therefore, this hill’s new listed summit height is 395.5m and this was derived from LIDAR analysis, this is 6.5m higher compared to its previously listed summit height of 389m which is adjoined to a triangulation pillar that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and 3.5m higher than the 392m spot height given the previous qualifying hill of Lord’s Seat.

The full details for the hill are:

Group:  The Cheviot

Name:  Green Side

OS 1:50,000 map:  80

Summit Height (New Height):  395.5m (LIDAR)

Summit Grid Reference:  NT 90695 07602 (LIDAR)

Col Height: 339.5m (LIDAR)

Col Grid Reference:  NT 90531 07919 (LIDAR)

Drop:  56.0m (LIDAR)

Myrddyn Phillips and Aled Williams (August 2020)