[Tagging] layer=-1, rivers, bridges and tunnels

Peter Wendorff wendorff at uni-paderborn.de
Sat Mar 15 13:01:27 UTC 2014


I agree partially with you here.
Yes, adding bridges in addition to the road is possible and may be a
good idea.
What we currently map as being a bridge in fact is the property of "the
road is on a bridge" instead.
Changing the current tagging scheme to "duplicate the corresponding
segment of the way and tag the bridge as a separate, but again linear
object" is worse in all but one point.
The only point this is better in is that a street with a continuous name
may not have to be splitted because of the bridge; but on the other hand
we do so for anything else, too: speed restrictions, footway or not,
highway type, surface and anything else; so it doesn't solve an issue
dedicated to bridges.

On the other hand it doesn't solve the issue with multiple parallel ways
on the same bridge, e.g. considering a dual carriage way on one bridge
construction we currently map the property "road is on a bridge" again
on both parts of the dual carriage way independently, but it's
impossible to decide from the data (usually) if it's one bridge or two
Your proposal to duplicate the way does not solve this issue either, as
you would still need two separate ways here.


Am 15.03.2014 13:25, schrieb André Pirard:
> Hi,
> I wonder why we make bridges split and split and split the roads.
> In reality, bridges are pieces of concrete or stonework at level -1
> under an uninterrupted foil of tarmac at level 0.
> Or at level 0 if it's understood that the renderer knows what's a bridge.
> And the renderer knows, as it draws two thin stripes beside the road.
> So, a bridge can be a little way segment overlaying the road.
> This lets the routing software ignore the unnecessary complication of
> having to account for bridges as part of the route.
> This lets the bridge having its own attributes, unrelated to the road,
> for example a different name.
> This makes obsolete discussions wondering if the bridge must be split in
> two because the road changes in the middle.
> Etc. etc., all pieces clutch in very neatly.
> And BTW, this is similar to tunnel=culvert which is an optional feature
> of a bridge and that surprises no one at layer -1.
> And now, if we put bridges and culverts at -1, the rivers or streams are
> normally at -2.
> Tunnels (inside which the road runs) should be segments too, at level +1
> or 0.
> I have tagged a number of streams and rivers at -2 -1 0 and I find it
> appreciable to have an instant view of where the complete main stream
> is, if not exaggeratedly long, as well as less prone to errors.
> Cheers,
> André.
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