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

 

Pt. 474.4m (NY 381 113) 

There has been a Significant Height Revision to a hill that was considered for listing 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 derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Pt. 474.4m (NY 381 113)

The criteria for the list that this height revision applies to 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 list is a sub list entitled the Sub-Fours, the criteria for which are all English hills at or above 400m and below 500m in height that have 15m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available to download in Google Doc format from the Mapping Mountains site.

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

The hill is being listed by the point (Pt. 474.4m) notation, and it is adjoined to the Helvellyn group of hills, which are situated in the English Lake District, and it is positioned with the A591 road to its west and the A592 road to its east, and has the village of Glenridding towards the north.

When the Introduction to the first group of hills for the updated and revised listing of the The Fours – The 400m Hills of England was published by Mapping Mountains on the 10^th September 2022, it was announced that the accompanying sub lists were being revised with the two 390m categories dispensed with and the criteria and name of the 400m Sub-Fours revised.  The one accompanying sub list is now named the Sub-Fours with its criteria being all English hills 400m and above and below 500m in height that have 15m and more and below 30m of drop.

Prior to this revision this hill was listed with an estimated c 15m of drop, based on an estimated c 472m summit height and an estimated c 457m col height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

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

However, it was not until LIDAR became available that the details for this hill 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. 

LIDAR summit image of Pt. 474.4m (NY 381 113)

LIDAR analysis gives the height of this hill as 474.4m positioned at NY 38179 11348, and when compared to its originally listed summit height this 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 height and Ordnance Survey, Harvey or other interactive 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 with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 474.4m and this was derived from LIDAR analysis, this is 2.4m higher than the originally listed c 472m summit height, which was based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Helvellyn

Name:  Pt. 474.4m

OS 1:50,000 map:  90

Summit Height (New Height):  474.4m (LIDAR)

Summit Grid Reference:  NY 38179 11348 (LIDAR)

Col Height:  460.9m (LIDAR)

Col Grid Reference:  NY 38166 11274 (LIDAR)

Drop:  13.5m (LIDAR)

 

Myrddyn Phillips and Aled Williams (April 2025)