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

Pt. 501.4m (SH 730 397) – Uchaf addition

There has been an addition to the listing of The Welsh Highlands – Uchafion Cymru, with the summit height, bwlch height and their locations, the drop and status of the hill confirmed by a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips and Aled Williams on the 19^th July 2020 and aerial map comparisons.

Pt. 501.4m (SH 730 397)

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

The Welsh Highlands – Uchafion Cymru – This is the revised draft title for the Welsh 500m P15s list that takes in all hills in Wales at or above 500m in height with 15m minimum drop.  The list is co-authored by Myrddyn Phillips and Aled Williams with the Introduction to the list being published on Mapping Mountains in November 2015 and an update relating to the list appearing on Mapping Mountains on the 19th June 2019.

The Welsh Highlands - Uchafion Cymru by Myrddyn Phillips and Aled Williams

For now the hill is being listed by the point (Pt. 501.4m) notation, and it is adjoined to the Arenig Fach group of hills, which are situated in the central part of North Wales (Region A, Sub-Region A3), 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 Trawsfynydd towards the south-west.

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 small 500m ring contour and bwlch contouring between 480m – 490m that appear on the Ordnance Survey 1:25,000 Explorer map its interpolated drop value was judged insufficient for either Uchaf or 500m Sub-Uchaf status.

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

Since the original compilation of this list 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 mapping on the WalkLakes website and the Magic Maps website.

Extract from the WalkLakes website

One of the mapping resources 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 a 504m spot height is given on the area of its summit.

Another resource available online is the interactive mapping originated from Ordnance Survey data hosted on the Magic Maps website.  This mapping also shows a 504m spot height on the summit area of this hill.

Extract from the Magic Maps website

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.  This resulted in its bwlch height being estimated as c 488m based on interpolation of 5m contouring between 485m – 490m.

Extract from the OS Maps website

The hill was first proposed as an Uchaf by Myrddyn Phillips and Aled Williams subsequently analysed the hill as follows:

Summit height of c 500m at SH 73026 39780 interpolated from OS paper maps.  Bwlch position estimated from QGIS modelling of OS Terrain 50 data to be c 487m at SH 72991 39724.  Enlarged-scale online OS maps give a summit height of 504m, which may be the result of a data modelling error caused by the forestry.

However, it was not until the survey with the Trimble GeoXH 6000 that the details for this hill could be accurately re-assessed.  The summit of this hill and a number of potential bwlch positions were subsequently surveyed, with the bwlch height and position given for this hill having been obtained from the data spread produced from the various bwlch surveys and scrutiny of aerial map comparisons.

At the summit of Pt. 501.4m

Gathering data during one of a number of surveys for the bwlch position of Pt. 501.4m

Therefore, the addition of this hill to Uchaf status is due to a Trimble GeoXH 6000 survey and aerial map comparisons, resulting in a 501.4m summit height and a 485.5m bwlch height, with these values giving this hill 15.9m of drop, which is sufficient for it to be classified as an Uchaf.

The full details for the hill are:

Group:  Arenig Fach

Name:  Pt. 501.4m

OS 1:50,000 map:  124

Summit Height:  501.4m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SH 73011 39784 (Trimble GeoXH 6000)

Bwlch Height:  485.5m (Trimble GeoXH 6000 data set spread)

Bwlch Grid Reference:  SH 73105 39632 (from aerial map comparisons) 

  

Drop:  15.9m (Trimble GeoXH 6000 summit and Trimble GeoXH 6000 bwlch data set spread) 

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

The Welsh 500m P15s (Yr Uchafion)

The Welsh 500m P15s (Yr Uchafion) – 500m Subs

The Welsh 500m P15s (Yr Uchafion) – 490m Subs

The Welsh 500m P15s (Yr Uchafion) – Double Subs

Myrddyn Phillips and Aled Williams (November 2020)