> The key issue with that approach: how does a mapper who isn't expert > enough to grade accurately the difficulty of a MTB trail, but can > clearly see, 'a road bike wouldn't work here', tag the thing > appropriately? Simple 'highway=path foot=yes bicycle=yes' invites > routing disasters. I can, and do, add 'surface=ground > smoothness=horrible', but is that enough? How many tags must a router > take into consideration before deciding that a cycleway is actually > usable? >
This is not the correct tagging anyway for a (countryside or mountain) path, at least for those countries where the default access for highway=path implies bicycle=yes and horse=yes (legal access!). And: the router should ignore the bicycle=yes tag on a highway=path. highway=path on its own does not imply any indication about the suitability for using it on foot, on bicycle, or on horse. The suitability can be indicated by a variety of tags: surface; smoothness; sac:scale; mtb:scale; incline; width; trail_visibility (leaving aside the special cases of bicycle|foot=designated|official which are, unfortunately, an established way of tagging mixed foot-cycle paths in general) The mapper should insert those tags that she can assess on the ground or from other available sources. It is these tags that a trekking bicycle router should assess: it should put a severe penalty on highpath=path without any additional tagging, or with bad surface, or with steep incline, or with mtb:scale>0, or with poor trail_visibility. it should assign a very low penalty to a highway=path with bicycle=designated, or to highway=cycleway (most likely my tag examples are not complete, but this illustrates the concept)
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