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

sergio sevillano sergiosevillano.mail at gmail.com
Fri Jan 23 08:50:25 GMT 2009

80n escribió:
> David
> 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.
> 80n
> On Thu, Jan 22, 2009 at 8:21 PM, Matthias Julius <lists at julius-net.net 
> <mailto:lists at julius-net.net>> wrote:
>     Chris Hill <chillly809 at yahoo.co.uk
>     <mailto: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
im with Mattias here.
if there is air under the way i tag it as bridge, leaving the ramps out.
the layer of the way gives you the hint of the existance or not of ramps.

if the way is "layer=0" and the bridge is "layer=1" there is a ramp.

if the way is "layer=0" and the bridge is "layer=0" too
(the crossing way under is "layer=-1", digged)
then the bridge has no ramps.

so if we want to give more detail as to describe the ramp,
i would just tag the ramp as "bridge_ramp=yes"
and the airborn part of the way leave it as "bridge=yes"

i dont think there is need, as 80n said,
to tag all parts as "bridge=yes"
and then differentiate "main_span" and "bridge_ramp"

my two cents please
sergio sevillano
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