Mapping Mountains – Hill Reclassifications – The Welsh Highlands - Uchafion Cymru

Iwerddon (SH 686 479) – Welsh Highland P15 addition

There has been an addition to the listing of the The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill derived from detail on contemporary maps produced from Ordnance Survey data, with confirmation from subsequent LIDAR analysis conducted by Aled Williams.

Iwerddon (SH 686 479)

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

Welsh Highlands – Uchafion Cymru – Welsh hills at or above 500m in height with 15m minimum drop, with an accompanying sub list entitled the Welsh Highland Subs, the criteria for which is all Welsh hills at or above 500m in height with 10m or more and below 15m of drop.  This list is authored by Myrddyn Phillips and Aled Williams with the Introduction to the list published on Mapping Mountains in November 2015 and the latest update relating to the list published on Mapping Mountains in January 2023.

Welsh Highlands - Uchafion Cymru by Aled Williams and Myrddyn Phillips

The name the hill is listed by is Iwerddon and it is adjoined to the Moelwyn Mawr group of hills, which are situated in the north-western part of North Wales (Region A, Sub-Region A2), and it is positioned with the A487 and the A496 roads to its south and the A470 road to its east, and has the town of Blaenau Ffestiniog towards the south-east.

This hill was not included in the original list of Welsh 500m P15s that later became known as Yr Uchafion and latterly as The Welsh Highlands – Uchafion Cymru, as with a 570m uppermost ring contour and no summit spot height and bwlch contouring between 560m – 570m that appear on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map, it was difficult through interpolation to give this hill an estimated drop value.

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

Since the original compilation of this list there are now a number of interactive maps originated from Ordnance Survey data that are available online.  One of these is the mapping on the Magic Maps website, and this map gives this hill a summit spot height of 579m which is positioned at SH 68671 47997.

Extract from the Magic Maps website

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 this hill it also shows the 579m summit spot height.

Extract from the WalkLakes map

The details for this hill were re-examined when the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map became available online.  This mapping had many spot heights not on any other publicly available Ordnance Survey map and its non-contour map also gives a 579m summit spot height.

Extract from the Ordnance Survey non-contour Vector Map Local hosted on the Geograph 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.  This mapping has an uppermost 575m ring contour and bwlch contouring between 560m – 565m, with interpolation giving an estimated c 564m bwlch height.

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 Uchaf status is due to LIDAR analysis, resulting in a 578.7m summit height and a 561.8m bwlch height, with these values giving this hill 16.9m of drop, which is sufficient for it to be classified as an Uchaf.

The full details for the hill are:

Group:  Moelwyn Mawr

Name:  Iwerddon

OS 1:50,000 map:  115

Summit Height:  578.7m (LIDAR)

Summit Grid Reference:  SH 68673 47996 (LIDAR)

Bwlch Height:  561.8m (LIDAR)

Bwlch Grid Reference:  SH 68726 48082 (LIDAR) 

  

Drop:  16.9m (LIDAR)

 

For the additions, deletions and reclassifications to The Welsh Highlands – Uchafion Cymru reported on Mapping Mountains please consult the following Change Registers:

 Welsh Highland P15s

Welsh Highland Subs

Myrddyn Phillips and Aled Williams (July 2020)