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

Bryn Crwn (SH 785 456) – 400m Sub-Pedwar addition

There has been an addition to the listing of Y Pedwarau - The 400m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill initially derived from analysis of data on the Geograph and WalkLakes websites, coupled with the 5m contouring on the OS Maps website, and with confirmation via subsequent LIDAR analysis conducted by Myrddyn Phillips.

LIDAR image of Bryn Crwn (SH 785 456)

The criteria for the list that this addition 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 list are five categories of sub hills, with this hill being included in the 400m Sub-Pedwar category.  The criteria for this sub category 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.

Y Pedwarau - The 400m Hills of Wales by Myrddyn Phillips and Aled Williams

The name the hill is listed by is Bryn Crwn, and it is adjoined to the Arenig Fach group of hills, which are situated in the central part of North Wales (Region C1, Sub-Region C1A), and it is positioned with a minor road to its west and the B4407 road to its south and has Llyn Conwy to its north-west, and has the village of Penmachno towards the north and Ysbyty Ifan towards the north-east.

Prior to analysis of data on the Geograph and WalkLakes websites this hill was listed with an estimated c 19m of drop, based on the 487m summit spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map and an estimated c 468m bwlch height, based on interpolation of 10m contouring between 460m – 470m.

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

The details for this hill were re-assessed when the Ordnance Survey non-contour Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map became available online.  This mapping has many spot heights not on other publicly available Ordnance Survey maps and importantly for this hill it has a 488m summit spot height positioned over 130 metres from where the 487m spot height appears on the Ordnance Survey 1:25,000 Explorer map indicating a higher position within the uppermost contour.

Another resource now available online is the WalkLakes website which hosts an interactive map originated from the Ordnance Survey Open Data programme.  This map has many spot heights not on other publicly available Ordnance Survey maps and for the summit of this hill the 488m spot height also appears in the same position as it does on the non-contour Vector Map Local hosted on the Geograph website.

Extract from the interactive mapping hosted on the WalkLakes website

The details for this hill were also 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.  These re-assessments resulted in the hill being listed with an estimated c 20m of drop.

Extract from the OS Maps website

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Therefore, the confirmation of the addition of this hill to 400m Sub-Pedwar status is due to LIDAR analysis, resulting in a 488.6m summit height and a 468.5m bwlch height, with these values giving this hill 20.1m of drop, which is sufficient for it to be classified as a 400m Sub-Pedwar. 

The full details for the hill are:

Group:  Arenig Fach

 

Name:  Bryn Crwn

OS 1:50,000 map:  115

Summit Height:  488.6m (LIDAR)

Summit Grid Reference:  SH 78586 45680 (LIDAR)

Bwlch Height:  468.5m (LIDAR)

Bwlch Grid Reference:  SH 78524 46104 (LIDAR)

Drop:  20.1m

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 (December 2019)