Mapping Mountains – Hill Reclassifications – Y Pedwarau – The 400m Hills of Wales

Cyrnau (SN 735 536) – 400m Sub-Pedwar deletion

There has been a deletion to the listing of the Y Pedwarau – The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail on contemporary Ordnance Survey maps.

The criteria for the list that this deletion applies to are:

Y Pedwarau – The 400m Hills of Wales.  Welsh hills at or above 400m and below 500m in height that have 30m minimum drop, accompanying the main Y Pedwarau list are five categories of sub hills, with this hill being deleted from the 400m Sub-Pedwar category.  The criteria for 400m Sub-Pedwar status being all Welsh hills at or above 400m and below 500m in height that have 20m or more and below 30m of drop.  The list is co-authored by Myrddyn Phillips and Aled Williams and is published on Mapping Mountains in Google Doc format.

The name the hill is listed by is Cyrnau, and it is adjoined to the Elenydd group of hills, which are situated in the northern part of Mid and West Wales (Region B, Sub-Region B2), and it is positioned with a minor road to its north-west and south, and has the town of Tregaron towards the north-west.

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

When the 1^st edition of the Y Pedwarau was published by Europeaklist in May 2013, this hill was listed as a 400m Sub-Pedwar with an estimated c 20m of drop, based on the 446m summit height that appeared as a spot height on the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage map and an estimated c 426m bwlch height based on interpolation of 10m contouring between 420m – 430m on the Ordnance Survey 1:25,000 Explorer map.  The 446m summit spot height is also shown on Ordnance Survey data that appears on the Magic Maps website. 

Extract from the Magic Maps website

The details for this hill were re-assessed when the OS Maps website became available online.  This is the replacement for OS Get-a-map and has contours at 5m intervals which are proving consistently more accurate compared to the 5m contours that sometimes appear on Ordnance Survey 1:25,000 Explorer maps and used to appear on the online Vector Map Local.  This re-assessment resulted in the hill being listed with an estimated c 427m bwlch height based on interpolation of 5m contouring between 425m – 430m, resulting in the drop value decreasing to an estimated c 19m. 

Extract from the OS Maps website

Therefore, the deletion of this hill from 400m Sub-Pedwar status is due to re-assessment of detail on contemporary Ordnance Survey maps, resulting in a 446m summit height and an estimated c 427m bwlch height, with these values giving this hill c 19m of drop which is insufficient for it to be classified as a 400m Sub-Pedwar.

The full details for the hill are:

Group:  Elenydd 

Name:  Cyrnau

OS 1:50,000 map:  146, 147

Summit Height:  446m (spot height)

Summit Grid Reference:  SN 73549 53650 (spot height)

Bwlch Height:  c 427 (interpolation)

Bwlch Grid Reference:  SN 73606 53426 (interpolation)

Drop:  c 19m (spot height summit and interpolated bwlch)

For the additions, reclassifications and deletions to Y Pedwarau – The 400m Hills of Wales reported on Mapping Mountains since the May 2013 publication of the list by Europeaklist please consult the following Change Registers:

Y Pedwarau

Y Pedwarau – 400m Sub-Pedwarau

Y Pedwarau – 390m Sub-Pedwarau

Y Pedwarau – 390m Double Sub-Pedwarau

Myrddyn Phillips and Aled Williams (March 2020)