Mapping Mountains – Hill Reclassifications – 200m Twmpau

Cae Cefn Tŷ (SN 416 535) – 200m Sub-Twmpau reclassified to 200m Twmpau

There has been a reclassification to the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail on contemporary and historical maps produced from Ordnance Survey data.  This was initiated by Joe Nuttall who produced a summit analysis programme, and then by evaluation conducted by Jim Bloomer and subsequently by Myrddyn Phillips.

The criteria for the list that this reclassification 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, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward.

The 200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Cae Cefn Tŷ and this was derived from the Tithe map, and it is adjoined to the Hafod Ithel group of hills which are situated in the western part of Mid and West Wales (Region B, Sub-Region B2), and it has the A487 road to its north-west, the B4338 road to its south-west and minor roads to its south-east and its north-east, and has the town of Ceinewydd (New Quay) towards the north north-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. 

When 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 with an estimated c 25m of drop, based on the 289m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 264m bwlch height, with the latter based on interpolation of 5m contouring between 260m – 265m.

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

The Ordnance Survey 1:25,000 Explorer map shows Cae Cefn Tŷ to be a twin 289m map heighted hill along with its adjacent hill of Moel Rhydeinon (SN 427 542), which for listing purposes was prioritised for the main summit and therefore the lowest connecting bwlch, due to it having a triangulation pillar on its summit area and an OS Bolt given the height of 290.254m in the OS Trig Database that appear as B/Bolt POSS OK.  This Database also reports that the trig station was removed by the farmer.

Since publication of these P30 lists on Geoff Crowder’s v-g.me website there have been a number of Ordnance Survey 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 are current and digitally updated such as the old Vector Map Local that used to be hosted on the Geograph website and which was entitled the Interactive Coverage Map, and it is the series of Six-Inch maps and the Historical 1:25,000 map that shows an imperial height of 953ft (290.48m) for Cae Cefn Tŷ and a 951ft (289.87m) height for Moel Rhydeinon.  These summit heights resulted in the swapping of the bwlch positions. 

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

The details for this hill were also re-assessed against the mapping on the OS Maps website.  This is the replacement for OS Get-a-map and until recent times had contours at 5m intervals which were proving consistently more accurate compared to the 5m contours that sometimes appear on the Ordnance Survey 1:25,000 Explorer map and used to appear on the online Vector Map Local.  The contouring on this mapping did not match that on the Ordnance Survey 1:25,000 Explorer map, but it is being prioritised for this hill and resulted in its bwlch height being listed as an estimated c 258m based on interpolation of 5m contouring between 255m – 260m.

Extract from the OS Maps website

Therefore, the reclassification of this hill from 200m Sub-Twmpau status is due to detail on contemporary and historical maps produced from Ordnance Survey data, resulting in a 290m summit height and an estimated c 258m bwlch height, with these values giving this hill an estimated c 32m of drop, which is sufficient for it to be classified as a 200m Twmpau.

The full details for the hill are:

Group:  Hafod Ithel

Name:  Cae Cefn Tŷ

OS 1:50,000 map:  146

Summit Height:  290m (spot height)

Summit Grid Reference:  SN 41694 53513 (hand-held GPS via DoBIH)

Bwlch Height:  c 258m (interpolation)

Bwlch Grid Reference:  SN 40762 52700 (interpolation)

Drop:  c 32m (spot height summit and interpolated bwlch)

Myrddyn Phillips (November 2020)