Mapping Mountains – Summit Relocations – The Welsh P15s

 

Tyn Ffynnon (SN 549 487) 

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 Tyn Ffynnon (SN 549 487)

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 listed by is Tyn Ffynnon and this was derived from the Tithe map and it is adjoined to the Mynydd Bach group of hills, which are situated in the western part of South Wales (Region B, Sub-Region B1), and it is positioned encircled by minor roads, with the B4337 road farther to its west, the A475 road farther to its south and the A482 road farther to its east, and has the town of Llanbedr Pont Steffan (Lampeter) towards the east south-east.

When the listing that became known as The Welsh P15s was being compiled, this hill was included in the main P15 list with an estimated c 16m of drop, based on the 224m summit spot height positioned at SN 55020 48780 that appears on the Ordnance Survey 1:50,000 Landranger map and 1:25,000 Explorer map and an estimated c 208m bwlch height, based on interpolation of 5m contouring between 205m - 210m that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage 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 224.4m positioned at SN 54973 48741.  However, this is a part 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 Tyn Ffynnon (SN 549 487)

The height produced by LIDAR analysis to the natural summit of this hill is 224.3m positioned at SN 54956 48738, and this position in relation to the raised field boundary comes within the parameters of the Summit Relocations used within this page heading, these parameters are:

The term Summit Relocations applies to when the high point of the hill is positioned in a different field, to a different feature such as a conifer plantation, within a different map contour, a different point where a number of potential summit positions are within close proximity, when natural ground or the natural and intact summit 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 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 224.3m and this is to the natural summit of the hill which is positioned at SN 54956 48738, 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 70 metres south-westward from where the 224m spot height appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map and 17 metres westward from where the high point of the raised field boundary is positioned.

 

The full details for the hill are: 

Group:  Mynydd Bach 

Name:  Tyn Ffynnon 

OS 1:50,000 map:  146

Summit Height:  224.3m (LIDAR)                                                           

Summit Grid Reference (New Position):  SN 54956 48738 (LIDAR) 

Bwlch Height:  210.0m (LIDAR) 

Bwlch Grid Reference:  SN 55631 48720 (LIDAR) 

Drop:  14.3m (LIDAR) 

 

Myrddyn Phillips (December 2022)