Marhofn 212.12 - May 2010

A Certain Ratio

Jim Bloomer

It was on a cold April day on Sgurr Dhomhnuill in 2008 that the 1.2.5 idea took shape. I'd been working with Roddy Urquhart of the UK Metric Association, trying to develop a system of classifying the UK's hills in a way that might, ultimately, attract some hillwalkers away from their pre-occupation with 2000-footers and 3000-footers. Before that day, we'd developed a system for the UK with 158 summits with a prominence of 500 metres or more, most with subsidiary P200 and P100s over 500m height; a total of 1562 hills. This three-tier approach delivered what we wanted; it allowed us to sort our hills into a hierarchy by prominence, so that the relationship between important (P500) summits and their less important (P200 and P100) descendants could be understood and easily presented.

What the system failed to offer was a way to incorporate lesser summits in the UK and, more importantly, the more mountainous parts of our planet. The 1.2.5 prominence hierarchy system works for the World, the Himalayas, Alps, Great Britain, Lakes, Norfolk or your local park. The principle is a geometric progression based on the best approximation to the cube root of ten, and it is no coincidence that it also forms the basis for coinage and banknotes in almost all countries. If you ally the 1.2.5 system with some thinking about the backbone or watershed of any landmass (however large or small), then you can start to formulate a plan for a World Mountain Catalogue (WMC). If we can develop a numeric code for the human genome and life, then we can perhaps start to plan how to represent our planet's topography in a logical format.

Marhofn readers are likely to be sympathetic to the view that the primary feature of a hill or mountain is its prominence (or drop). Munro, with his 'separate mountain' and 'tops', first introduced the idea of a hill hierarchy. Donald and Bridge followed with rules relating to distance and prominence, and Dawson, in his Hewitts publications, established the P30 category as a subsidiary of P150.

As a fan of modern mapping and the use of metres in particular, it's with some reluctance that I point out that P30 and P150 fit the 1.2.5 system applied in feet. Using Dawson's sensible approximations, 1.2.5 in feet becomes 3.6.15 in metres. Now the 3.6.15 system might find favour in the UK and USA but, whilst full of heritage, it is a metric system built on an imperial foundation and, as a cross-breed, perhaps less likely to find international favour in the long term.

One thing the 1.2.5 system does is simplify complex hill groups. Reducing the Pennines to Cross Fell or the greater Cairngorms to Ben Macdui, Ben Rinnes, Lochnagar and Beinn a'Ghlo may be a novel approach but it allows complexity to be unravelled.

Cross Fell has the largest territory in the UK and its footprint extends from the Tyne to the cliffs of Dover (Kinder Scout just fails to qualify as a P500). Even the most insignificant pimple in Kent can be linked back to its ancestor in the northern Pennines. From Sutherland to the Cotswolds, Britain has an east/west watershed. There are precise points where a raindrop will either travel to the North Sea or alternatively the Irish or Hebridean Sea. This watershed line is highly convoluted and passes over hundreds of summits. With the 1.2.5 system you can see that this line passes through the territory of just 38 P500s, together with Carn Eige (P1000). The watershed line needs to be defined accurately for the WMC to work. The solution is to use the most northerly and southerly points of any landmass. Dunnet Head sits within the territory of the P500 Morven, and Lizard Point is similarly related to High Willhays. In the WMC, we number Morven 01, Ben Hee 02 through to High Willhays at 39. Think of these 39 hills (or more strictly their territories) as forming the trunk of a tree and consider that 97 other hills form the branches and sub-branches (or vertebrae and ribs if you prefer). Mainland Britain has 24 westerly branches (ribs) formed by the territories of 75 P500s and two P1000s (Ben Nevis and Snowdon). There are 11 easterly branches comprising 20 P500s.

The landmass of Eurasia and Africa has similar trunk and branch characteristics. The trunk descends from Siberia's northerly tip near Chelyuskin to Cape Agulhas in the western Cape. Two P5000s (Everest and Kilimanjaro) and 186 P2000s define this landmass, and their resolution to trunk and branches is a similar task to that of applying it to mainland Britain, but with higher mountains separated by larger distances. Landmasses can be categorised according to the prominence of their highest point. Thus, whilst Britain is a third-category landmass, Sicily and Corsica with their P2000 summits are second category and considered to be in the 'North Atlantic' for WMC purposes. The only first-category landmasses are Eurasia/Africa and the Americas. Arran is fourth category and Lundy merely sixth category.

The ability to simplify any landmass allows us to construct the framework for the WMC, and with rapidly improving map data a worthwhile catalogue should become constructible. Within the context of the WMC, the British mainland can be deconstructed to just 02.03.03.58.39E20W77 - the 02 indicates it is in the North Atlantic; the 03 that it's on a third-category landmass (most prominent hill is a P1000); 03.58 is the latitude and longitude of Dunnet Head in whole degrees; it has 39 hills in its trunk, 20 hills making up its easterly branches and 77 its westerly branches. Now consider my nearest hill, Dow Crag in the Coniston fells. Its unique code is 02.03.03.58.38W02.03.07 - the first eight digits are as defined above then 38W02 defines Scafell Pike (38 is Cross Fell, 38W01 Helvellyn, 38W01N01 Skiddaw and 38W03 Grasmoor); 03 indicates that Coniston Old Man is the third most prominent hill in the Scafell Pike family; finally the 07 indicates that Dow Crag is the seventh most prominent hill in the Coniston Old Man family. By adding extra pairs of digits you can delve deeper into the local topography, studying P50s, P20s and even P10s.

Roddy Urquhart and I are in the process of updating the website www.prominentpeaks.org.uk which currently deals primarily with UK hills over 500m. You can contact the author through this site to find out more.