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

 

Rippon Tor (SX 746 755) 

There has been a Significant Height Revision that is retrospective 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 conducted by Myrddyn Phillips. 

LIDAR image of Rippon Tor (SX 746 755)

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 Rippon Tor, 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 B3387 road to its north and minor roads to its west and south-east, and has the town of Bovey Tracey towards the east north-east. 

Extract from the Ordnance Survey 1:50,000 Landranger map

When the listing that is now known as The Fours – The 400m Hills of England was originally compiled by Myrddyn Phillips, this hill was listed with a 473m summit height, based on the spot height that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

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

When the 1^st edition of the The Fours now co-authored by Myrddyn Phillips and Aled Williams was published by Europeaklist in December 2013 the summit height was amended to 477m, with an accompanying note stating:

Summit height from 1,563.8ft (476.65m [476.47m height relative to Ordnance Datum Newlyn]) levelled height on Ordnance Survey 1:2,500 map which matches the rounded up 1,564ft height on the Ordnance Survey New Popular One-Inch map.  The imperial height of 1,563ft (476.4m [476.2m height relative to Ordnance Datum Newlyn]) is also recorded on the Ordnance Survey Seventh Series One-Inch map.  Summit height of 473m on current Ordnance Survey 1:50,000 and 1:25,000 map.  Triangulation pillar with 475.905m flush bracket height on summit area.  The trig pillar is positioned within a wind shelter and is built on a concrete base with the ground at the base of the trig being approximately 475.555m - 475.605m in height, and as the high point of this hill is a substantial slab of rock positioned a few metres from the wind shelter and an approximate 1m higher than the base of the trig, the listed height of 477m can also be calculated from 475.6m (base of trig) + 1m = 476.6m.  However, there's still an unusual 3.6m discrepancy in the current 473m Ordnance Survey map height.

When the 2^nd edition of The Fours – The 400m Hills of England co-authored by Myrddyn Phillips and Aled Williams was published by Mapping Mountains Publications in April 2018, the height of this hill was reassessed and it was listed as 476m, with an accompanying note stating:

476m summit height taken from the 1,563.8ft (476.65m) surface height on the OS Six-Inch map published in 1886.  Triangulation pillar with 475.905m flush bracket height situated on the summit area and positioned in a wind shelter with its flush bracket 60cm lower than the summit of the hill, this corresponds with the 476.47m surface height relative to Ordnance Datum Newlyn.  However, there is still an unusual 3.5m discrepancy between the 476.47m height and the current 473m OS map height.

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 Rippon Tor (SX 746 755)

LIDAR analysis gives the highest ground on this hill as 476.3m positioned at SX 74661 75574, 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 476.3m and this was derived from LIDAR analysis, this is 3.3m higher than its originally listed 473m summit height, which appears as a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

 

The full details for the hill are:

Group:  Broad Barrow

Name:  Rippon Tor

OS 1:50,000 map:  191

Summit Height (New Height):  476.3m (LIDAR)

Summit Grid Reference:  SX 74661 75574 (LIDAR)

Col Height:  357.6m (LIDAR)

Col Grid Reference:  SX 73917 79116 (LIDAR)

Drop:  118.7m (LIDAR)

 

Myrddyn Phillips and Aled Williams (March 2024)