Mapping Mountains – Significant Name Changes – 100m Twmpau

 

Coed Bryn Glas (SN 746 997) 

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 Coed Bryn Glas (SN 746 997)

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.  The list is authored by Myrddyn Phillips, 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 Banc Llechwedd Mawr group of hills, which are situated in the north-western part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north-east, west and east, the A489 road to its north and the A487 road to its north-west, and has the town of Machynlleth towards the north.

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 it was considered not to meet the criteria then used for this sub category.

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. 189m) notation with an estimated c 22m of drop, based on the 189m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 167m bwlch height, based on interpolation of 10m contouring between 160m – 170m. 

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

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 position the name of Coed Bryn Glas to land where the summit of this hill is situated.

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

 

The full details for the hill are:

Group:  Banc Llechwedd Mawr

Name:  Coed Bryn Glas

Previously Listed Name:  Pt. 189m   

OS 1:50,000 map:  135

Summit Height:  188.0m (LIDAR) 

Summit Grid Reference:  SN 74685 99743 (LIDAR) 

Bwlch Height:  161.4m (LIDAR) 

Bwlch Grid Reference:  SN 74592 99604 (LIDAR) 

Drop:  26.6m (LIDAR) 

 

Myrddyn Phillips (April 2025)