[Tagging] Tunnels and bridges

Steve Bennett stevagewp at gmail.com
Fri Feb 1 07:03:13 GMT 2013

A few problems with the current approach:
1) When several things pass over the same bridge (eg,
highway=secondary, highway=cycleway and highway=footway; or even just
two independent lanes), renderers currently draw multiple bridges.

2) In areas where structures (buildings, paved areas, piers,
riverbanks) are mapped precisely, bridges can't be - they're assumed
to be the width of a standard road.

3) Bridges have distinct properties (name, height, etc) that can't be
modelled properly because bridges don't actually exist. Tags like
bridge_name are a kludge that don't work in cases like 1).

These are all problems worth fixing.

The solution seems to be:
a) (Optional Create a relation that can group things together
(type=bridge, or something more general if there's something good)
b) (Optional) Create a closed way for the bridge itself, and tag it
with a new tag (probably man_made=bridge would be best, because it
would be better rendered by naive renderers than say building=bridge)
c) (Optional) Add the bridge, if mapped, to the relation.

It seems that every time this topic comes up, people want to go too
far, and find general solutions (eg, solving both bridges and tunnels
at once with "across" and "over" relation memberships), and start
solving other problems too (eg, 3D buildings, not splitting ways when
they pass over bridges...). It all gets complicated, and everyone
gives up.

But the solution above is pretty simple, and doesn't require breaking
anything, and is totally optional. Map the way you do currently if you
want, or also map the bridge separately if you want, or use a
relation, or both.


On Fri, Feb 1, 2013 at 10:01 AM, Michael Kugelmann <MichaelK_OSM at gmx.de> wrote:
> On 31.01.2013 12:06, Martin Vonwald wrote:
>> 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
> The current  method is used and well established since years and for my
> point of view works fine. So I clearly dislike to change it.
> Just my 2 cents,
> Michael.
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