Saturday, 14 January 2017

Change Register - The Welsh 500m P15s - 490m Subs

Change Register

The Welsh 500m P15s
490m Subs

All hills in Wales at or above 500m in height with a minimum prominence of 15m; from the 500m summit of Esgair Saeson to the 1085m summit of Yr Wyddfa

The Welsh 500m P15s is a hill list co-authored by Myrddyn Phillips and Aled Williams, and was first announced on the Mapping Mountains site on 4th November 2015 where a complete breakdown of hill totals was listed by Group.  The list then comprised of 630 hills within the main list that met the qualifying criteria with over 100 of these hills making their first known appearance in any form of hill list; emphasising the fact that this listing is the most comprehensive of its kind for this height band of hill in Wales.

The listing originated in 2004 at which time it included a sub category for those hills that met the qualifying height but only had 14m or more and below 15m of drop, these are now known as the 500m Subs.  This listing now includes two other sub categories; the 490m Subs and the Double Subs and this Change Register details those hills that are, or have been listed within the 490m Subs category.

The 490m Subs are those hills that fail to meet the Welsh 500m P15 qualification by 10m or less of height, these are the hills that are 490m or more and below 500m in height that have a minimum 15m of drop.

Since ‘The Welsh 500m P15s listing originated it has developed ever since with it now being co-authored with Aled Williams, having the two other sub categories within it, and having over 330 marginal hills surveyed using a basic levelling technique.  It is now also benefiting from the accurate surveys conducted with GPS / GNSS receiver, an expanded range of Ordnance Survey maps available online and most recently, by analysis of LIDAR data.

However, it is not just numerical data that has seen this list develop since its first inception, it is also place-name data, and it was because of this and their mutual interest in hill lists that the authors first corresponded.

In recent years, acronyms or short monikers referring to specific hill lists have become increasingly popular in hill-walking circles, and during the compilation of ‘The Welsh 500m P15s’ the authors have used the Welsh word ‘Uchaf (Higher)’ to refer to these hills, with the plural being ‘Uchafion’, since these summits take in the higher tier of the Welsh uplands.  This moniker will be used on the Mapping Mountains site to refer to this class of hill.

It seems fitting that the list of ‘The Welsh 500m P15s – 490m Subs should now benefit from a detailed Change Register, and although the hill list in its entirety is not yet published it is prudent for this Change Register to initially detail the changes to this sub category since the November 2015 introduction published on the Mapping Mountains site.

The Change Register to ‘The Welsh 500m P15s – 490m Subs appears below with the reclassifications to the 490m Subs list being detailed chronologically in receding order.

Change Register

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

Pt. 499.1m    499.1m at SN 86343 76073

This hill’s reclassification from an Uchaf was announced on the Mapping Mountains site on the 13.03.17, with the hill previously listed with an estimated c 500m summit height based on the flatness of the summit area in relation to the small uppermost 500m ring contour on Ordnance Survey maps.  The hill’s reclassification to a 490m Sub-Uchaf is due to analysis of LIDAR data by Aled Williams, with the resulting 499.1m summit height being too low for the hill to qualify as an Uchaf490m Sub-Uchaf total increases by one and confirmed as 62.


Twynau Gwynion    496.2m at SO 06765 10699

This hill’s reclassification was announced on the Mapping Mountains site on 10.01.17, with the hill previously listed as a 490m Sub-Uchaf with 16m of drop based on the 498m summit spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and a 482m bwlch spot height on the Ordnance Survey enlarged mapping hosted on the Geograph website.  This hill was reclassified from a 490m Sub-Uchaf to a Double Sub-Uchaf from LIDAR data analysed by Aled Williams, resulting in the hill having a 496.2m summit and 481.3m bwlch height, with these values giving this hill 14.9m of drop which is insufficient for this hill to retain its 490m Sub-Uchaf status.  490m Sub-Uchaf total decreases by one and confirmed as 61.   

4th November 2015 – Mapping Mountains first publishes details to ‘The Welsh 500m P15s – 490m Subs

490m Subs total confirmed as 62.

Myrddyn Phillips and Aled Williams (January 2017)

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