[Tagging] Tunnels and bridges

Tobias Knerr osm at tobias-knerr.de
Fri Feb 1 08:30:39 GMT 2013

On 01.02.2013 07:22, Martin Vonwald (imagic) 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?

Because it is usually _not_ the case that all the features within the
bridge outline polygon belong to the bridge.

There are other reasons - for one, not all sides of the outline polygon
are created equal, as some connect to the ground and others are bridge
"edges". This is actually an important distinction for rendering. Still,
the most clear difference is likely the one mentioned above.


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