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

Black Hill (SX 761 786)

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 derived from LIDAR analysis initially conducted by Aled Williams and subsequently by Myrddyn Phillips. 

LIDAR image of Black Hill (SX 761 786)

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 list are three categories of sub hills, the 400m Sub-Four category, the 390m Sub-Four category and the 390m Double Sub-Four category.  The list is co-authored by Myrddyn Phillips and Aled Williams and the 2^nd edition of the booklet containing this list was published by Mapping Mountains Publications on the 24^th April 2018.

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

The name the hill is listed by is Black Hill, and it is adjoined to the Broad Barrow group of hills, which are situated in Dartmoor in the south-west of the country, and it is positioned with the A382 road to its north-east and the A38 road to its south south-east, and has the village of Widecombe-in-the-Moor to the west south-west and the town of Bovey Tracey to the east.

When the 1^st edition of the The Fours was published by Europeaklist in December 2013, this hill was listed with an estimated c 31m of drop, based on the 412m summit spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map and an estimated c 381m col height, based on interpolation of 10m contouring between 380m – 390m.

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 Black Hill (SX 761 786)

LIDAR analysis gives the highest ground on this hill as 414.2m positioned at SX 76101 78646, and 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 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.

Therefore, the new listed summit height of this hill is 414.2m and this was derived from LIDAR analysis, this is 2.2m higher than its previously listed height of 412m which appears as a spot height on the Ordnance Survey 1:25,000 Explorer map.

The full details for the hill are:

Group:  Broad Barrow

Name:  Black Hill

OS 1:50,000 map:  191

Summit Height (New Height):  414.2m (LIDAR)

Summit Grid Reference:  SX 76101 78646 (LIDAR) 

  

Col Height:  381.0m (LIDAR)

Col Grid Reference:  SX 75841 77803 (LIDAR)

Drop:  33.2m (LIDAR)

Myrddyn Phillips and Aled Williams (June 2018)