[Tagging] Meaning of access=yes on highway=footway?

[Minh Nguyen]

Vào lúc 04:27 2022-04-25, Florian Lohoff đã viết:
> PS: Not that i think tagging anything with agricultural makes ANY sense
> as the farmer knows his farmland and does not care about access
> tags in OSM, he/she will not even use it. Everybody else is not
> affected.

Yes, we're spilling a lot of ink on the finer points of possibly moot 
edge cases. We could say that vehicle=agricultural overrides the 
vehicle=no implied by highway=footway, but does anyone envision building 
a tractor router based on OSM data anytime soon?

The original question was seemingly more straightforward: can access=yes 
override the standard meaning of a primary feature tag like 
highway=footway? It was occasioned by an unintuitive route from OsmAnd, 
so we know it's a real-world problem.

This world never ceases to surprise me, so I wouldn't categorically rule 
out an occasional need to override the semantics that a layperson would 
attribute to a word like "footway". But more specific access tags like 
vehicle=yes are already adequate for achieving this override. Between a 
footway that all of creation may trample upon and a footway that *only* 
allows pedestrians and "all land-based vehicles" to traverse -- that's a 
difference without a distinction.

Routers disagree about highway=footway access=yes. For example, OSRM 
routes cars over it, at least as a last resort [1], but GraphHopper has 
country-specific profiles for Austria and Germany that explicitly do 
not. [2][3] Meanwhile, I'm unaware of any renderer that distinguishes it 
from a bare highway=footway to let users know that they may drive on the 
footway.

I suggest we take a classic software architecture copout: call this 
combination *undefined behavior*, let data consumers interpret it 
however they please, encourage mappers to avoid it in favor of something 
more predictable, and move on to other things.

[1] 
https://github.com/Project-OSRM/osrm-backend/blob/79d4363d5972ea4d69abd92b26cda80de7941365/features/car/access.feature#L290
[2] 
https://github.com/graphhopper/graphhopper/blob/b94bcbb39d8a912618a34971fe09cc0d332f4d4d/core/src/main/java/com/graphhopper/routing/util/countryrules/AustriaCountryRule.java#L70
[3] 
https://github.com/graphhopper/graphhopper/blob/b94bcbb39d8a912618a34971fe09cc0d332f4d4d/core/src/main/java/com/graphhopper/routing/util/countryrules/GermanyCountryRule.java#L78

-- 
minh at nguyen.cincinnati.oh.us