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

DUE TO SUBSEQUENT LIDAR ANALYSIS THIS HILL HAS BEEN DELETED FROM 400m SUB-PEDWAR STATUS

Mynydd Tynant (SH 751 407) – 400m Sub-Pedwar addition

There has been an addition 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 maps derived from Ordnance Survey data.

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 added to 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 Mynydd Tynant, 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 the B4391 road to its north, the A470 road to its west and the A4212 road to its south, and has the village of Ffestiniog towards the west north-west.

Prior to analysis of data on the Geograph and WalkLakes websites this hill was not classified as the contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map give it an uppermost 430m ring contour and bwlch contouring between 420m – 430m, implying it does not have sufficient drop for 400m Sub-Pedwar status.

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 437m summit spot height positioned at SH 75146 40791.   

Extract from the Ordnance Survey non-contour Vector Map Local hosted on the Geograph website

Another resource now available online is the WalkLakes website which hosts an interactive Ordnance Survey 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 this hill’s summit the 437m 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

Therefore, the addition of this hill to 400m Sub-Pedwar status is due to the analysis of data on the Geograph and WalkLakes websites with the estimated bwlch height derived from 5m contouring on the OS Maps website.  Resulting in this hill being listed with a 437m summit height that appears as a spot height on the non-contour Vector Map Local hosted on the Geograph website and on the WalkLakes website and an estimated c 417m bwlch height, based on 5m contouring between 415m – 420m on the OS Maps website, with these values giving this hill an estimated c 20m of drop, which is sufficient for 400m Sub-Pedwar status.

The full details for the hill are:

Group:  Arenig Fach 

Name:  Mynydd Tynant

OS 1:50,000 map:  124

Summit Height:  437m (spot height)

Summit Grid Reference:  SH 75146 40791 (spot height)

Bwlch Height:  c 417m (interpolation)

Bwlch Grid Reference:  SH 75126 40688 (interpolation)

Drop:  c 20m (spot height summit and interpolation 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 (January 2020)