Mapping Mountains – Significant Height Revisions – Welsh Highlands – Uchafion Cymru

Clo Cadno (SO 118 162) 

There has been a Significant Height Revision to a hill that is listed in the Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Aled Williams. 

Clo Cadno (SO 118 162)

The criteria for the list that this height revision applies to are:

Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop.  This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Clo Cadno and it is adjoined to the Cefn yr Ystrad group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and is positioned with minor roads to its north-west and south-west and the B4560 road to its east, and has the village of Llangynidr towards the north-east and the small community of Trefil towards the south. 

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

When the list that later became known as the Welsh Highlands – Uchafion Cymru was first compiled, this hill was not included as the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map have an uppermost 520m ring contour with bwlch contouring between 510m – 520m. 

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

The details for this hill were re-examined via mapping on the OS Maps website.  This is the replacement for OS Get-a-map and had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000 Explorer map and the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map, and this mapping indicated that this hill had a minimum of 15m of drop. 

Extract from the interactive mapping that was hosted on the OS Maps website

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 image of Clo Cadno (SN 118 162)

LIDAR analysis gives the highest ground on this hill as 530.3m positioned at SO 11849 16247, 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 530.3m and this was derived from LIDAR analysis, this is 10.3m higher than the uppermost 520m ring contour that appears on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Cefn yr Ystrad

Name:  Clo Cadno

OS 1:50,000 map:  161

Summit Height (New Height):  530.3m (LIDAR) 

Summit Grid Reference:  SO 11849 16247 (LIDAR)

Bwlch Height:  513.6m (LIDAR)

Bwlch Grid Reference:  SO 12197 15992 (LIDAR)   

Drop:  16.7m (LIDAR) 

 

Myrddyn Phillips and Aled Williams (October 2023)