Mapping Mountains – Summit Relocations – The Welsh P15s

Lan Fawr (SN 420 147) 

There has been a Summit Relocation to a hill that is listed in the 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 Lan Fawr (SN 420 147)

The criteria for the list that this summit relocation applies to 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 Lan Fawr, and this was derived from the Tithe map, and it is adjoined to the Mynydd Sylen group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with a minor road to its north and south-east, the A484 road to its west and the B4309 road to its east, and has the town of Caerfyrddin (Carmarthen) towards the north.

When the listing that became known as The Welsh P15s was being compiled, this hill was included in the main list with 15m of drop, based on the 139m summit spot height adjoined to a triangulation pillar positioned at SN 42032 14695 that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, and the 124m bwlch spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

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 analysis gives the highest ground on this hill as 140.5m positioned at SN 42209 14782.  However, this is to the top of a raised track and protocols dictate that as this is deemed a relatively recent man-made construct such ground is discounted from the height of a hill. 

LIDAR summit image of Llan Fawr (SN 420 147)

The height produced by LIDAR analysis to the summit of this hill is 139.7m and is positioned at SN 42050 14708 and SN 42058 14704, and this comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies when the high point of the hill is found to be positioned; in a different field, to a different feature such as in a conifer plantation,  within a different map contour either on Ordnance Survey maps or interactive mapping, to a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit of a hill is confirmed compared to a higher point such as a raised field boundary or covered reservoir that is considered a relatively recent man-made construct, or the de-twinning of a summit, or a relocation of approximately 100 metres or more in distance from either the position of a map spot height or from where the summit of the hill was previously thought to exist.

Therefore, the summit height produced by LIDAR analysis is 139.7m and is positioned at SN 42050 14708 and SN 42058 14704, this position is not given a spot height on the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and is approximately 18 metres north-eastward from where the triangulation pillar is positioned and approximately 159 metres west south-westward from where the high point of the raised track is positioned. 

 

The full details for the hill are: 

Group:  Mynydd Sylen 

Name:  Lan Fawr 

OS 1:50,000 map:  159

Summit Height:  139.7m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 42050 14708 & SN 42058 14704 (LIDAR)

Bwlch Height:  123.3m (LIDAR) 

Bwlch Grid Reference:  SN 43780 15743 (LIDAR) 

Drop:  16.5m (LIDAR) 

 

Myrddyn Phillips (May 2025)