Compiling the Welsh P15s - the Ultimate Tick List?

After eight years of research, Myrddyn Phillips has finally completed the list of summits in Wales with a 15 metre prominence. At a massive 5866 entries, this must be the ultimate Welsh mega-list. Any takers?


When I first discovered the beauty that the British uplands have to offer, I longed for those dark winter nights when maps were unfolded, guidebooks read and routes plotted to hitherto unvisited hills. Plotting these routes gave me an appreciation of Ordnance Survey (OS) maps, and although route plotting was the main aim, the maps themselves also took on a special beauty all of their own.

The view from the summit of Gurn Wigau, a P15 in the Carneddau in north Wales  © Myrddyn Phillips
The view from the summit of Gurn Wigau, a P15 in the Carneddau in north Wales
© Myrddyn Phillips

I began to view OS maps as a work of art; they are also life savers as many hill walkers have experienced. My study of OS maps soon went beyond mere route plotting, as I indulged in what would become a passion for hill classification.

This passion would not exist without the greater joy of getting out on the hill, and it will always be the latter that drives me. However, the prospect of map study and hill classification soon took hold in ways that I could not then envisage.

Hill classification is dependent upon contours and spot heights on OS maps, and without these, few of the hill lists that many hill walkers enjoy, would exist. It is also dependent upon set criteria, as without this a list becomes arbitrary in nature.

In Britain the quaint double-use of imperial and metric measurement is evidenced even in hill classification, as what has become known as P30s have taken hold within the hill bagging community.

For the uninitiated a P30 is a hill that has a minimum 30m of prominence above its connecting col to the next higher hill along the watershed. With the 'P' standing for prominence, also known as drop, and the '30' standing for the height difference in metres between summit and connecting col. The quaintness comes from the fact that 30m is based on the nearest whole numbered metric equivalent of 100ft.

One of the first hill lists I set out to compile were the remaining P30s to Wales. The P30 hills above 500m in height had already been listed by Alan Dawson (Hewitts) and Michael Dewey (500m Tops) with Terry Marsh also incorporating P30 within his Welsh 600m guide book. All that remained were the hills below 500m in height. Sounds a simple thing to do, but about 2,500 of them had yet to be listed, and the compilation of these remaining P30s took a long time to complete.

A patchwork of greens and purples with P15 hills on Moel Garegog  © Myrddyn Phillips
A patchwork of greens and purples with P15 hills on Moel Garegog
© Myrddyn Phillips

My Welsh P30 lists incorporated a P20 sub-list of hills; however, the accompanying sub-list was not standard as it did not use interpolated height, took Ordnance Survey spot heights as fact and only included hills that once surveyed stood a chance of entering the main P30 list.

Soon after compiling these Welsh P30 lists I completed a list to the Welsh P15 hills at or above 500m in height, with the intention to carry on listing to P15 for other height bands of Welsh hills. Times have changed since these lists originated, as our former reliance upon OS 1:25,000 paper mapping has evolved to varied mapping resources now available online for any budding hill list compiler, including historic OS Six-Inch and One-Inch maps. However, it was not until the advent of an OS map hosted on the Geograph website that my aim to map the whole of Wales down to P15 could start in earnest. This map is known as the Vector Map Local and titled the Interactive Coverage Map on the Geograph website, and its advantage over other publicly available maps is the inclusion of many spot heights that are exclusive just to this map. For list compilers it seemed their Christmases and birthdays had all arrived at once!

The OS map on the Geograph website and its inclusion of otherwise unknown and all-important spot heights meant that the compilation of my next height band of hills could be attempted. These were the 400m P15s of Wales and soon after their completion I turned my attention to the 300m height band.

Ynys Llanddwyn is one of the gems of the Welsh P15s  © Myrddyn Phillips
Ynys Llanddwyn is one of the gems of the Welsh P15s
© Myrddyn Phillips

When compiling the Welsh P15 hills at or above 500m in height I created an accompanying P14 sub-list. I contemplated creating a P12 or even P10 sub-list, but realised this would be too reliant upon interpolation and would increase the work load substantially. The concept of a P14 sub-list was therefore also employed as I started on the other height bands of P15 hills.

In the process of completing the 400m and 300m height band of P15s I had also fully revised two P30 lists that would become known as Y Pedwarau – The 400m Hills of Wales and Y Trichant – The 300m Hills of Wales, with the former now co-authored with Aled Williams.

The details I noted during compilation of the Welsh P15s include an appropriate name for the hill and its connecting col (if known), their heights and ten figure grid reference and the all-important drop value.

I started listing the Welsh 200m P15s in the middle of November 2013 and completed the last group of hills in August 2014. This 200m height band of P15s proved to have the greatest number of hills of any 100m height band in Wales.

During the latter part of 2013 I invested in a Trimble GeoXH 6000 and activated a blog named Mapping Mountains, and much of my hill related activity was now directed through these media. With my attention now concentrated on surveying hills with the Trimble and writing articles for Mapping Mountains, progress on the remaining height bands of Welsh P15s inevitably slowed.

I started compilation on the 100m height band of Welsh P15s in October 2013 and soon opted to compile the hill groups within the 15-99m height band of hills immediately after completing their 100m counterparts. This dual height band form of compilation remained during the next 3½ years until full completion.

Ynys Arw; a P15 amongst Ynysoedd y Moelrhoniaid (The Skerries) which are situated to the north-west of Ynys Môn (Anglesey  © Myrddyn Phillips
Ynys Arw; a P15 amongst Ynysoedd y Moelrhoniaid (The Skerries) which are situated to the north-west of Ynys Môn (Anglesey
© Myrddyn Phillips

When compiling the original Welsh P30s I found the 30-99m height band to be the most difficult to list and envisioned the same would apply to their P15 counterparts. The main reason for this is that lower heighted contours stretch for greater distances and by doing so are more difficult to follow, resulting in adjoining cols being more difficult to pinpoint compared to their higher counterparts, and sure enough it was the 15-99m height band of Welsh P15s adjoined to the Ynys Môn (Anglesey) group of hills that proved the most difficult of all to compile as the land taking in this group is relatively low in height but also large in area.

During the latter stages of compiling the Welsh P15s the Ordnance Survey 5m contouring on the OS Maps website became available online, and this mapping was then used to cross reference against the mapping on the Geograph website.

The other major resource that became available during this overall compilation is LIDAR (Light Detecting & Ranging). This has revolutionised list compilation in ways that only independent surveyors can match, and all conducted from the comfort of a chair in front of a laptop screen; the times they are indeed a' changing!

The 100m height band of Welsh P15s was finally completed in April of this year, closely followed by their 15-99m counterparts in early May. When I listed the last hill and completed the whole of Wales mapped down to P15 (mapped down to P14 with the inclusion of the subs) I looked at the online mapping I had been studying and with a relieved smile closed the tab on my laptop and filed the last page of hill details in their folder.

The Welsh P15 list has taken me over 8 years to complete, with about a year dedicated to the hills at or above 500m in height and the remaining height bands being compiled from 2012 onwards.

The bi-product of listing down to P15 with accompanying P14 subs has resulted in the discovery of many new P30 hills, it has standardised their accompanying P20 sub-list and also resulted in a Double Sub list that now accompanies the Welsh Twmpau P30 list. Although these are important bi-products of the Welsh P15s, it is this larger list that holds forth as its overall number of 5866 hills is vast compared to any other previous listing of Welsh hills, with the inclusion of over 2,800 hills never before listed and classified.

The current totals for the height bands as they were compiled are:

  • P15s at or above 500m: 631 hills with 26 P14 subs
  • 400m P15s: 872 hills with 68 P14 subs
  • 300m P15s: 1083 hills with 78 P14 subs
  • 200m P15s: 1138 hills with 88 P14 subs
  • 100m P15s: 995 hills with 94 P14 subs
  • 15m – 99m P15s: 712 hills with 81 P14 subs

The Welsh P15s comprise 5431 hills with 435 P14 subs.

Hats off to the first person to bag all those!


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