Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

 

Banc (SN 721 762) 

There has been a Significant Height Revision to a hill that is listed in the Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis and a subsequent Trimble GeoXH 6000 survey conducted by Myrddyn Phillips. 

Banc (SN 721 762)

The criteria for the list this height revision affects are:

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Banc and this was derived from the Tithe map, and it is adjoined to the Elenydd group of hills which are situated in the central part of the Mid and West Wales Region (Region B, Sub-Region B2), and it is encircled by minor roads with farther afield the A4120 road to its north and the B4343 road to its east, and has the village of Pontarfynach (Devil’s Bridge) towards the east north-east. 

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website this hill was not included in the Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 22m of drop based on the 350m summit spot height and the 328m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.  The 350m summit spot height is now shown on the interactive mapping available on the Magic Maps website with the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps only showing an uppermost 340m ring contour. 

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 Banc

LIDAR analysis gives the summit height of this hill as 350.75m, and as the summit has now been surveyed with the Trimble GeoXH 6000 it is this result that is being prioritised for listing purposes 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 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. 

The Trimble GeoXH 6000 gathering data at the summit of Banc

Therefore, this hill’s new listed summit height is 350.9m and this was derived from a Trimble GeoXH 6000 survey, this is 10.9m higher than the uppermost 340m ring contour that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps. 

 

The full details for the hill are: 

Group:  Elenydd 

Name:  Banc 

OS 1:50,000 map:  135, 147

Summit Height (New Height):  350.9 (converted to OSGM15, Trimble GeoXH 6000) 

Summit Grid Reference:  SN 72127 76209 (Trimble GeoXH 6000) 

Bwlch Height:  329.1m (LIDAR) 

Bwlch Grid Reference:  SN 72361 75991 (LIDAR) 

Drop:  21.7m (Trimble GeoXH 6000 summit and LIDAR bwlch) 

 

Myrddyn Phillips (May 2021)