[Tagging] Tunnels and bridges

[Martin Koppenhoefer]

2013/1/31 Martin Vonwald <imagic.osm at gmail.com>:
> Hi!
>
> I'm looking for some alternatives to map tunnels and bridges that
> contain several ways. I'm not really happy with the proposed relation
> [1]. Is there any other approach for this? I'm asking myself why don't
> we simply map the outline of the bridge/tunnel (the latter may be more
> difficult to obtain), tag it with something like structure=bridge (or
> similar, maybe even building=bridge), bridge=<type> (if necessary) and
> layer=x. Connect the ways running over the bridge to this structure,
> use the same layer tag and you're set. It is after all a physical
> object, so why don't we map it as such? I simply don't see any reason
> for a relation here.


+1, drawing the outline seems a good approach as it permits to group
visually (and topologically) different carriageways running over the
same bridge (as opposed to two parallel bridges). Actually a "classic"
bridge will often have several outlines when the abutments are mapped
separately, and then you would use layer-tags and maybe would want to
also add the abutments to the bridge-object (in this case a relation
might be needed). For tunnels I am not sure if there are situations
with several carriageways in the same tube (in this case a common
outline made sense IMHO, while 2 parallel tubes should be (IMHO)
considered 2 tunnels. Tunnels also have the practical problem that you
can't see their inside on aerial imagery and GPS doesn't work inside,
but this is a different issue aside from tagging.

Whether "building" is a nice key might be disputable (a bridge
technically isn't a building, but a technical structure, on the other
hand I have always argued that "building" in OSM is a generic tag for
all kind structures and not only those intended for humans to live
inside), but personally I'd approve it. If we decide to use building=*
for bridges the * should be always the same value (e.g. "bridge") and
not building=draw_bridge etc. (these details like bridge typology
would go into subtags, allowing easy filtering of the bridges if you
don't want to render them as buildings).

These bridge-objects would also allow us to tag in an easy and
standard way stuff like ref-numbers and bridge names (i.e. with "ref"
and "name" and not requiring stuff like "bridge_name"...), have a
common object to link WP-articles, etc.

Cheers,
Martin