[OSM-talk] When is a bridge not a bridge?

80n 80n80n at gmail.com
Thu Jan 22 22:50:40 GMT 2009

Was there a specific purpose you had in mind that needs to distinguish
between the main span of a bridge and it's ramps, or were you just exploring
the level of consistency in current tagging practices?

I wonder if we are approaching this problem from the right direction.

There are currently about 250,000 ways that are tagged bridge=yes.  Since
there's no generally agreed definition of the extent of a bridge every user
will have used a different assumption and their own judgement.

Perhaps we should keep the vague and approximate definition that the bridge
tag provides, and instead propose extra tags that more precisely define the
lesser characteristics of a bridge.  The bridge tag as it currently exists,
for all its vagueness, is easy to use and effective.

For more precision we could consider additional tags that precisely define
the individual parts of a bridge.  The addition of a bridge_ramp tag, for
example, could be used to indicate whether or not a bridge includes or
excludes the ramps.

bridge=yes, bridge_ramp=included|excluded

For those that want to define the extent of the ramps specifically then a
separate way would be required for each ramp and for the main span, perhaps
like this:

bridge=yes, bridge_ramp=yes
bridge=yes, main_span=yes
bridge=yes, bridge_ramp=yes

However, I'm not sure such an elaborate scheme would catch on much unless
there's a real benefit in tagging bridges to a greater  level of detail.
That's why I wondered whether you have a specific reason for wanting to tag
bridges with more precision.


On Thu, Jan 22, 2009 at 8:21 PM, Matthias Julius <lists at julius-net.net>wrote:

> Chris Hill <chillly809 at yahoo.co.uk> writes:
> > A bridge is usually there to cross something.  So I would say,
> > generally, what ever was built or built-up or added to make the bridge
> > function is part of the bridge.  So ramps or approaches on embankments
> > even might well be judged to be part of the bridge.  Maybe a note
> > attached to briefly describe your decision will help future OSMers.  As
> > always there are exceptions.
> I'd day when there is air under the road it is part of the bridge, if
> there is only a pile of dirt it is not part of the bridge.  Even if
> the dirt has been specifically piled up there to be able to get on top
> of the bridge.
> Matthias
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