Mapping Mountains – Significant Height Revisions – Y Pedwarau – The 400m Hills of Wales and Y Pellennig – The Remotest Hills of Wales

Ffridd Ddu (SH 726 064) 

There has been a Significant Height Revision to a hill that is listed in the Y Pedwarau – The 400m Hills of Wales and Y Pellennig – The Remotest Hills of Wales, with the summit height, bwlch height and their locations, the drop, remoteness and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Ffridd Ddu (SH 726 064)

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

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being listed in the 400m Sub-Pedwar category.  The criteria for 400m Sub-Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

Y Pellennig –The Remotest Hills of Wales - Welsh hills whose summit is at least 2.5km from the nearest paved public road and the hill has a minimum 15m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is available as a downloadable e-booklet or print-booklet version on Mapping Mountains Publications with the up-to-date master list available on Mapping Mountains to download in Google Doc format. 

Y Pellennig - The Remotest Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Ffridd Ddu and it is adjoined to the Tarren y Gesail group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with the B4405 road to its north-west and the A487 road to its east, and has the town of Machynlleth towards the south.

When the original 400m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category. 

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

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 20m of drop, based on the 433m summit spot height and the 413m 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.  These values also appeared for this hill when the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013 and the 1^st edition of Y Pellennig – The Remotest Hills of Wales was published by Europeaklist in April 2015. 

Extract from the interactive mapping hosted on the WalkLakes website

One of the mapping resources now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available maps and for this hill it also shows a 433m summit spot 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 Ffridd Ddu (SH 726 064)

LIDAR analysis gives the highest ground on this hill as 435.0m positioned at SH 72667 06467, 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 435.0m and this was derived from LIDAR analysis, this is 2.0m higher than the previously listed height of 435m which was based on the spot height that appeared on Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Tarren y Gesail

Name:  Ffridd Ddu

OS 1:50,000 map:  124

Summit Height (New Height):  435.0m (LIDAR)

Summit Grid Reference:  SH 72667 06467 (LIDAR)

Bwlch Height:  413.0m (LIDAR)

Bwlch Grid Reference:  SH 72593 06527 (LIDAR) 

Drop:  22.0m (LIDAR)

Remoteness:  2.590km

 

Myrddyn Phillips and Aled Williams (July 2023)