[Tagging] sidewalks and tagging for the renderer

Tobias Knerr osm at tobias-knerr.de
Fri Apr 13 08:27:33 BST 2012

Am 13.04.2012 08:20, schrieb Peter Wendorff:
> If we would define a set of defaults and mappers follow that set, nobody
> will add "default" values again, and it's not possible to distinguish
> between default and unknown any more.

You have identified a real problem: The distinction between default and
unknown values is lost with a default that is more than just a fallback
for programs. And I agree that certain tags with more than one commonly
used value should preferably be set explicitly everywhere.

However, I think that relying on defaults cannot really be avoided in
_all_ cases. For example, in many countries there are so few roads
usable only with 4wd vehicles that you will never see the default
explicitly tagged on all highways. Instead, you will have a small number
of roads tagged as "4wd only", and a lot of roads for which we just
assume not to have this restriction.

So for attributes that almost always have a certain value, I really
don't see any option except using that one as the default and accepting
that this makes "undefined" essentially impossible.

As a crude analogy: We don't add a node with "there's no shop here" at
every unoccupied coordinate either. Instead, we just treat unmapped
areas the same as areas where someone has already checked that there
really is no shop around. There are just too many coordinates without
shops, relatively speaking. And I think we will need to do the same for
rare attributes, too.


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