Mapping Mountains – Significant Name Changes – 100m Twmpau

Allt Pendugoedydd (SN 749 311) 

There has been a Significant Name Change to a hill that is listed in the 100m Twmpau, 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 Allt Pendugoedydd (SN 749 311)

The criteria for the list that this name change applies to are:100m Twmpau – Welsh hills at or above 100m and below 200m in height that have 30m minimum drop, with an accompanying sub list entitled the 100m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 100m and below 200m in height with 20m or more and below 30m of drop, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

100m Twmpau by Myrddyn Phillips

The hill is adjoined to the Mynydd Du group of hills, which are situated in the southern part of South Wales (Region B, Sub-Region B5), and it is positioned with the A4069 road to its north-west and minor roads to its west and east, and has the village of Llangadog towards the south-west.

When the original 100m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the Hills to be surveyed sub list, as with only an uppermost 150m contour on the contemporary Ordnance Survey 1:25,000 Explorer map, it was considered not to meet the criteria then used for this sub category. 

Extract from the Ordnance Survey 1:25,000 Explorer map

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-assessed and it was listed under the point (Pt. 163m) notation with an estimated c 20m of drop, based on the 163m summit spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and an estimated c 93m bwlch height, based on interpolation of 5m contouring between 90m – 95m that appeared on the OS Maps website.

Since the original publication of the Welsh P30 lists on Geoff Crowder’s v-g.me website there have been a number of maps made available online.  Some of these are historic such as the series of Six-Inch maps on the National Library of Scotland website.  Whilst others were digitally updated such as the Ordnance Survey Vector Map Local that was hosted on the Geograph website and which was entitled the Interactive Coverage Map, whilst others are current and digitally updated such as the interactive mapping on the Magic Maps and WalkLakes websites, and it is the series of Ordnance Survey Six-Inch maps that form the basis of the change in the listed name of this hill. 

Extract from the Ordnance Survey series of Six-Inch maps

The Ordnance Survey series of Six-Inch maps formed the base map Ordnance Survey used for many decades leading to the production of the 1:10,000 Series of maps, both have now been superseded by the digitised Master Map.  The series of Six-Inch maps are excellent for name placement and especially so compared to the contemporary Ordnance Survey 1:25,000 Explorer map, and it is the series of Six-Inch maps that place the name of Allt Pendugoedydd adjacent to the summit of this hill.

Therefore, the name this hill is now listed by in the 100m Twmpau is Allt Pendugoedydd, and this was derived from the Ordnance Survey series of Six-Inch maps. 

 

The full details for the hill are:

Group:  Mynydd Du

Name:  Allt Pendugoedydd

Previously Listed Name:  Pt. 163m   

OS 1:50,000 map:  146, 160

Summit Height:  162.4m (LIDAR) 

Summit Grid Reference:  SN 74992 31127 (LIDAR) 

Bwlch Height:  141.4m (LIDAR) 

Bwlch Grid Reference:  SN 75086 31369 (LIDAR) 

Drop:  21.0m (LIDAR) 

 

Myrddyn Phillips (April 2024)