The wiki contains some suggestions/guidelines about when to map
sidewalks as separate footways versus when to encode them as tags on the
main road. The basic recommendation seems to be that if there's a
barrier or even a strip of grass between the two, a separate way is fine
and even sometimes preferred (and the road should be tagged
sidewalk=separate to indicate that it's been mapped as a separate way),
but if the sidewalk is directly adjacent to the road, better to just
imply it with a sidewalk=left/right/both tag.
My gut tells me that a corollary should be: If the sidewalk on one side
of the road is mapped as a separate way, then the sidewalk on the other
side (if there is one) should also be a separate way, even if it's
directly adjacent to the road due to asymmetry of sidewalk design. Does
this sound right? I certainly don't see any clean way to tag a road to
indicate that one of its sidewalks has been mapped as its own way and
the other hasn't.
(My personal feeling is that that it's better to avoid mapping sidewalks
as separate ways unless there's a compelling reason that would outweigh
the additional data clutter and routing complications. In some
circumstances -- those where walking on the sidewalk, or on a particular
side of a road with two sidewalks, has noticeably different routing
implications -- it seems like a good idea.)
Thanks for you thoughts, jmb
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