Here’s the original thesis where that legend appears. Apparently it’s from an IGN TOP 25 map. Do you know if this is typical of French topographic maps?
What I find interesting about this legend is that it’s an entire scale of… not difficulty per se, but usability more holistically. To replicate this legend using OSM data, one would need to employ not only one of the keys like trail_visibility=* but multiple in concert. Or maybe “hard part of hiking trail” is relative to the trail itself rather than a universal scale?
Agreed. In other threads, I often come out against attempts to design bespoke typologies or abuse third-party scales, mainly because these attempts quickly turn out to be parochial and inflexible. (Hello, crossing=* and isced:level=*.) On the other hand, I do see value in intuitive, keyword-based keys to supplement more empirical keys about specific physical characteristics. The point of studying map legends is to ground the discussion: is a distinction so fundamental that it affects the very language that people use refer to the thing, even if they know nothing else about the thing?
One thing I’ve learned in studying legends for OSM Americana is the degree to which print cartographers play fast and loose with any physical characteristics they do mention. A seemingly straightforward scale of place labels sized by population – yet some cities actually get boosted or demoted based on notability. A seemingly precise specification of inclines by grade – but a reader will never fact-check the map for slight deviations from this criterion.