Tuesday, 17 January 2017

Change Register - The Welsh 500m P15s - Double Subs


Change Register

The Welsh 500m P15s
Double 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 Double Subs category.

The Double Subs are those hills that fail to meet the Welsh 500m P15 qualification by less than 10m of height and also less than 1m of drop, these are the hills that are 490m or more and below 500m in height and have 14m or more and below 15m of drop.

The Double Subs first appeared as a category of hill in the November 2015 announcement of the list on Mapping Mountains, and when the totals for each category were given there were five hills listed that met the qualification for Double Subs, all of these hills were identified leading up to this announcement.

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 – Double 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 – Double Subs appears below with the reclassifications to the Double Subs list being detailed chronologically in receding order.



Change Register

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






Banc yr Ŵyn    491m at SN 77182 92335

This hill’s deletion from the ranks of Double Sub-Uchafion was announced on Mapping Mountains on 11.05.17, with the hill previously listed with c 14m of drop based on the 491m summit spot height on the Ordnance Survey enlarged mapping hosted on the Geograph website and an estimated bwlch height of c 477m based on bwlch contouring between 470m – 480m.  Its subsequent deletion as a Double Sub-Uchaf is due to LIDAR data analysed by Aled Williams, resulting in the hill having a bwlch height of 478.1m and with no coverage of the summit position by LIDAR data the summit spot height is being used in conjunction with the bwlch data from LIDAR.  The resulting 13m of drop is insufficient for it to retain its Double Sub-Uchaf statusDouble Sub-Uchaf total decreases by one and confirmed as 5.   





Blaen yr Henbant    497.8m at SO 25412 21736

The addition of this hill to the ranks of Double Sub-Uchaf was announced on the Mapping Mountains site on the 16.04.17, with the hill previously considered not classified and catalogued with only 12m of drop based on its 498m summit spot height on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and the 486m bwlch spot height that appears on the Ordnance Survey enlarged mapping hosted on the Geograph website.  Its inclusion as a Double Sub-Uchaf is due to LIDAR data analysed by Aled Williams, resulting in the hill having a 497.8m (converted to OSGM15) summit and 483.0m (converted to OSGM15) bwlch height, with these values giving this hill 14.8m of drop which along with its summit height is sufficient for it to be classified as a Double Sub-Uchaf.  Double Sub-Uchaf total increases by one and confirmed as 6. 





Fowler’s Arm Chair    489.5m at SO 04122 79426

This hill’s deletion from the ranks of Double Sub-Uchaf was announced on the Mapping Mountains site on the 25.03.17, with the hill previously listed with an estimated summit height of c 491m based on the dimension of the uppermost 490m ring contour on Ordnance Survey maps, and with a 477m bwlch height taken from the Ordnance Survey enlarged mapping hosted on the Geograph website, with these values giving the hill an estimated c 14m of drop, which was sufficient for it to be classified as a Double Sub-Uchaf.  Its deletion from this category of sub hill is due to LIDAR data analysed by Aled Williams, resulting in the hill having a 489.5m summit and 476.4m bwlch height, with these values giving this hill 13.1m of drop which along with its summit height is insufficient for it to retain its Double Sub-Uchaf status.  Double Sub-Uchaf total decreases by one and confirmed as 5.   





Twynau Gwynion    496.2m at SO 06765 10699

The reclassification of this hill was announced on Mapping Mountains 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 qualifies it for Double Sub-Uchaf status.  Double Sub-Uchaf total increases by one and confirmed as 6.   
   

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


Double Subs total confirmed as 5.





Myrddyn Phillips and Aled Williams (January 2017)

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