From the trail's own tags on OpenStreetMap. IMBA's scale wins where it is mapped (easiest and easy are a green circle, more difficult a blue square, very difficult a black diamond, extremely difficult a double black). Otherwise the single-trail scale is read the way North American trail signs grade the same ground: S0 green, S1 blue, S2 black, S3 double black, S4 and up a pro line (the orange oval). A trail with no difficulty mapped is listed as unrated: it is still drawn, just without a sign or a colour of its own.
Oct 23, 2026