Mapping Mountains – Summit Relocations – The Welsh P15s

 

Cae Mawr (SN 462 175) 

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 Cae Mawr (SN 462 175)

This hill is also listed as the natural summit for a Dual Summit 100m Twmpau and a Dual Summit Lesser Dominant hill along with the man-made summit of Safle Claddu Nant y Caws (SN 468174 and SN 469 174).  However, this hill also qualifies as a Welsh P15, without the distinction of it being a Dual Summit hill, with its bwlch listed adjoined to the higher man-made summit.

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 Cae Mawr, 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 the A48 road to its north and a minor road to its south-west, and has the town of Caerfyrddin (Carmarthen) towards the north-west.

When the listing that became known as The Welsh P15s was being compiled, this hill was included in the main list with an estimated c 17m of drop, based on the 155m summit spot height adjoined to a triangulation pillar positioned at SN 46405 17608 that appears on the Ordnance Survey 1:50,000 Landranger andf 1:25,000 Explorer map, and an estimated c 138m bwlch height, based on interpolation of 5m contouring between 135m – 140m. 

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 156.3m positioned at SN 46256 17561.  However, this is to the top of a raised field boundary 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 Cae Mawr (SN 462 175)

The height produced by LIDAR analysis to the highest remaining natural ground of this hill is 155.1m and is positioned at SN 46268 17566, 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 155.1m and is positioned at SN 46268 17566, 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 137 metres west south-westward from where the originally listed summit is positioned and approximately 12 metres east north-eastward from the high point of the raised field boundary. 

 

The full details for the hill are: 

Group:  Mynydd Sylen 

Name:  Cae Mawr 

OS 1:50,000 map:  159

Summit Height:  155.1m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 46268 17566 (LIDAR)                                                  

Bwlch Height:  139.3m (LIDAR) 

Bwlch Grid Reference:  SN 46733 17459 (LIDAR) 

Drop:  15.8m (LIDAR) 

 

Myrddyn Phillips (May 2025)