[OSM-talk] Bridge tagging

[Gervase Markham]

I'm considering putting together the following proposal. As it's 
somewhat intrusive, I thought I'd post here first to see if there was 
significant opposition. A wide-ranging discussion is better accommodated 
on a mailing list than on a wiki page.

The proposal is to replace:

bridge=yes
waterway=aqueduct
highway=viaduct
railway=viaduct

with

bridge=yes
bridge=aqueduct
bridge=viaduct
bridge=swing
bridge=...

In other words, make all bridge-like structures values of the bridge 
tag. This would be acceptable on nodes and ways, although most instances 
would be on short-ish ways.

Advantages:

- Compatible with current usage of the "bridge" tag
- Mappers can use "bridge=yes" if they don't care, or be more specific
   if they like
- Renderers can have a generic bridge rendering and specialize if and
   when the learn particular values
- No more clashes with the highway/waterway tags

As someone said in the Viaduct change proposal:
"Viaducts are currently properties of the rail and highway tags, which 
is confusing. It also means you can't define the kind of highway or 
railway that the viaduct carries, which is pretty useless!"

Someone pointed out in the last discussion that a viaduct is technically 
not a bridge. _Technically_, this may be true, but I think the above 
suggested tagging scheme is highly understandable. Everyone knows what 
you mean.

Another option:

- Use bridge=yes for all types of bridge. But this loses important 
information - some renderers want to use a different icon e.g. for a 
swing bridge that you have to open by hand.

Relevant current proposals:
http://wiki.openstreetmap.org/index.php/Proposed_features/Viaduct
http://wiki.openstreetmap.org/index.php/Proposed_features/Aqueduct
http://wiki.openstreetmap.org/index.php/Proposed_features/Bridge_Type

Gerv