From Any tags you like on Wiki:
However, this does not mean “feel free to ignore existing tagging schemes and start marking pharmacies with unicorn=parking_lot”.
We may reasonably disagree if e.g. amenity=pharmacy
or healthcare=pharmacy
is better, but as long as data consumers recognize both as valid tags for the same thing, no harm done. However, we may not reasonably disagree about the scope of oneway
tag, since that introduces ambiguity and routers cannot discern with certainty what the mapper meant.
For the sake of argument, let’s assume the common example of shared sidewalk with one-way bicycle lane:
highway=footway
oneway=yes
bicycle=yes
…and, at some point, authorities decide to close it for cycle traffic entirely and put a sign to that effect. An unsuspecting mapper then only changes
bicycle=no
…and hey, changing that one tag suddenly means that oneway
refers to pedestrians! Sorry, but that’s… beyond weird. It borders on trolltaging:
Simply processing highway=cycleway, highway=path, highway=footway and standard access tags (especially bicycle=designated) should be enough to avoid listing fake ones. Data consumer in that situation should not be expected to check for proposed=yes, demolished=yes, construction=yes, completely_fictional=yes, operational_status=closed or end_date=1990.
While Wiki certainly should document how tags are used, it’s just as important to document how tags ought to be used. I’m afraid that some make the “any tags you like” principle into “tag however you are pleased”, which has never been the idea.
P.S. To clear any potential ambiguity: I think that either foot:backward=no
(which I find convoluted) or oneway:foot
to describe one-way pedestrian traffic is way superior than having oneway=yes
context-dependent.