Mapping Mountains – Summit Relocations – The Welsh P15s

 

Lan Ffynnon Las & Disgwylfa (SN 998 433) 

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 Ffynnon Las & Disgwylfa (SN 998 433)

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 Ffynnon Las & Disgwylfa, and this was derived from the Tithe map, and it is adjoined to the Mynydd Epynt group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with the B4519 road to its west and the B4520 road to its east, and has the hamlet of Capel Uchaf (Upper Chapel) towards the south south-east.

When the original 300m height band of Welsh P30 hills was published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list that accompanied the main P30 list, as it was considered not to meet the criteria then used for this sub category.

After the P30 lists were standardised, and interpolated heights and drop values also included, this hill was listed with an estimated c 20m of drop (with subsequent LIDAR analysis giving it 19.98m of drop) based on the 393m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 373m bwlch height based on interpolation of 10m contouring between 370m – 380m. 

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 392.3m positioned at SN 99808 43287.  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 Lan Ffynnon Las & Disgwylfa (SN 998 433)

The height produced by LIDAR analysis to the natural summit of this hill is 392.0m and is positioned at SN 99802 43305, 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 392.0m and is positioned at SN 99802 43305, 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 50 metres northward and placed in a different field from the position of the previously listed summit at the spot height, and approximately 18 metres north-westward from where the high point of the raised field boundary is positioned. 

 

The full details for the hill are: 

Group:  Mynydd Epynt 

Name:  Lan Ffynnon Las & Disgwylfa 

OS 1:50,000 map:  147, 160

Summit Height:  392.0m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 99802 43305 (LIDAR)

Bwlch Height:  372.0m (LIDAR) 

Bwlch Grid Reference:  SO 00000 43778 (LIDAR) 

Drop:  19.98m (LIDAR) 

 

Myrddyn Phillips (May 2025)