Mapping Mountains – Significant Name Changes – 200m Twmpau

Rhos Swydd (SO 117 650) 

There has been a Significant Name Change to a hill that is listed in the 200m 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 Rhos Swydd (SO 117 650)

The criteria for the list that this name change applies to are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m 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. 

200m Twmpau by Myrddyn Phillips

The hill is adjoined to the Fforest Glud group of hills, which are situated in the eastern part of South Wales (Region B, Sub-Region B3), and it is positioned with a minor road to its north-west, the A44 road to its south-west and the A488 road to its south-east, and has the town of Llandrindod towards the south-west.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying 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-evaluated and it was listed under the point (Pt. c 267m) notation with an estimated c 20m of drop, based on an estimated c 267m summit height and an estimated c 247m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

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 listed name of this hill.

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 Rhos Swydd to land where the summit of this hill is situated.

Extract from the Ordnance Survey series of Six-Inch maps

Therefore, the name this hill is now listed by in the 200m Twmpau is Rhos Swydd, and this was derived from the Ordnance Survey series of Six-Inch maps. 

 

The full details for the hill are:

Group:  Fforest Glud

Name:  Rhos Swydd

Previously Listed Name:  Pt. c 267m   

OS 1:50,000 map:  148

Summit Height:  268.0m (LIDAR) 

Summit Grid Reference:  SO 11706 65038 (LIDAR) 

Bwlch Height:  244.8m (LIDAR) 

Bwlch Grid Reference:  SO 12253 65143 (LIDAR) 

Drop:  23.2m (LIDAR)

 

Myrddyn Phillips (June 2026)