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

Matthias Julius lists at julius-net.net
Fri Jan 23 13:54:39 GMT 2009

Kenneth Gonsalves <lawgon at au-kbc.org> writes:

> On Friday 23 Jan 2009 6:00:08 pm Sven Rautenberg wrote:
>> > 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.
>> Something with negative layer has to be a tunnel. Bridges are useless if
>> there is a tunnel. Do not tag bridges as "layer=0" just because there
>> are no ramps. The layer tag is to help a renderer put the ways in the
>> right visual order - not to indicate whether or not a way is elevated or
>> not. Do not tag ways as "layer=-1" just because they are below the
>> general earth surface (such as rivers).
> this is important - only underground rivers should be given a -1 layer tag

Yes, it has been pointed out many times that layers are relative only
and have nothing to do with elevation.  They describe whether some
object is directly above another and not whether it is higher than
another one nearby.

Generally, I regard the earth's surface -- natural or not -- as
layer=0.  That means that a bridge which is completely level with the
surrounding area is still layer=1 (at least) because it is above the


More information about the talk mailing list