Mapping Mountains – Significant Height Revisions – The Welsh P15s

Y Faerdre (SH 784 795) 

There has been a Significant Height Revision to a hill that was listed in The Welsh P15s, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Y Faerdre (SH 784 795)

The criteria for the list that this hill used to be included in are:

The Welsh P15s – Welsh hills with 15m minimum drop, irrespective of their height, with an accompanying sub list entitled the Welsh Sub-P15s, with the criteria for this sub category being all Welsh hills with 14m or more and below 15m of drop.  The list is authored by Myrddyn Phillips, with the Introduction to the list appearing on Mapping Mountains on the 10^th May 2019. 

The Welsh P15s by Myrddyn Phillips

The name the hill is now listed by is Y Faerdre and this was derived from the Tithe map, and it is adjoined to the Mynydd Hiraethog group of hills, which are situated in the northern part of North Wales (Region A, Sub-Region A2), and it is positioned with the A546 road to its west and the B5115 road and the A470 road to its east, and has the town of Llandudno towards the south-east.

When the listing that became known as The Welsh P15s was being compiled, this hill was included in the P14 sub list with an estimated c 14m of drop, based on an estimated c 97m summit height and an estimated c 83m bwlch height, with both heights based on interpolation of 5m contouring. 

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 Y Faerdre (SH 784 795)

The summit height produced by LIDAR analysis is 93.2m and when compared to the originally listed summit height 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, Harvey or other interactive 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 with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 93.2m and this was derived from LIDAR analysis.  This is 3.8m lower than the estimated c 97m summit height previously lsited and which was derived from interpolation of the uppermost 95m contour ring that appeared on the 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:  Mynydd Hiraethog 

Name:  Y Faerdre 

OS 1:50,000 map:  115

Summit Height (New Height):  93.2m (LIDAR)                                                           

Summit Grid Reference:  SH 78472 79515 (LIDAR)                                                  

Bwlch Height:  81.1m (LIDAR) 

Bwlch Grid Reference:  SH 78520 79419 (LIDAR) 

Drop:  12.2m (LIDAR) 

 

Myrddyn Phillips (November 2024)