[Tagging] Tunnels and bridges

Steve Bennett stevagewp at gmail.com
Fri Feb 1 11:11:15 GMT 2013

On Fri, Feb 1, 2013 at 5:22 PM, Martin Vonwald (imagic)
<imagic.osm at gmail.com> wrote:
We have a spatial database so if all features are within a closed way
there is no need for a relation. Why is there a different reasoning
for a bridge?

Btw, is this actually true? Does the OSM API actually provide
functions to determine whether objects are within a way? And for
renderers working from local copies of the database, is it actually to
perform this calculation? My impression is that it's much much easier
to implement a relation look up (if "bridge" in x.relations.types...)
than a spatial look up (if x inside way with type "bridge").

I could be wrong, but I just wanted to check your assumption here. If
it's *possible* to do a spatial lookup, but more *difficult*, then
that's an argument in favour of relations rather than an implicit
spatial relationship.


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