[Tagging] Tunnels and bridges

Martin Vonwald imagic.osm at gmail.com
Fri Feb 1 10:18:29 GMT 2013

2013/2/1 Tobias Knerr <osm at tobias-knerr.de>:
> On 01.02.2013 09:49, Martin Vonwald wrote:
>> 2013/2/1 Tobias Knerr <osm at tobias-knerr.de>:
>>> 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.
>> For example? And I'm talking about features on the same level/layer.
> That's exactly the additional qualifier not present with the waterpark.
> But if we clearly define that
> - they must be on the *same* layer (==, not >=)
> - this layer must be explicitly tagged on the bridge itself
> - this layer must be explicitly tagged on all elements
> - ways must be split at the beginning and end of the bridge
> then the situation is probably still clear enough for data consumers.

That is exactly the way I intended it. I wrote it some posts earlier
that we should definitively keep the bridge and layer tags on the ways
themselves for backward compatibility. And if we drop the layer tag
(on the ways) we will lose the connection to the outline too.

> If I understand your reply to Steve today correctly (man_made=bridge
> outlines for one-level bridges), then you would be fine with requiring a
> relation for anything more complex, such as multiple levels or
> individually mapped piers and so on?

Correct. We will have three tagging variants which built on each
other. Simple bridge -> simple tagging. A little bit more complex ->
add a way and some tags. Really complex -> add a relation.

> In that case, this should be compatible with the rules outlined above,
> so if these are documented in this way I would be fine with it.



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