[OSM-talk] Layer transitions

["Marc Schütz"]

> > I want to talk about this page on the wiki describing how to map tunnels
> > correctly:
> > http://wiki.openstreetmap.org/wiki/Tunnel#How_to_Map
> >
> > Especially the last paragraph causes headaches to me:
> > "If the tunnel ends in a junction you'll need a small un-tunneled way
> > between the end of the tunnel and the junction"
> >
> >
> > Where does this rule come from?
> >
> this might be a logical topic: we are mapping the center of the road.
> The tunnel can not end at the center of the crossing road, because
> this road itself is not a tunnel. (you will have at least half the
> width of the crossing road untunneled).

No, IMO we're mapping the entire road, but represent it by a line located at the middle. This is a subtile but important difference; otherwise we wouldn't connect the incoming ways at a crossing, because they end at the edge of the road, not in the middle.

But I agree that in most cases there is a short way between the T junction and the tunnel/bridge, although I have encountered cases where a bridge started directly at the other road (give or take a few millimeters).
I think we should insert a "in most cases" into this rule.

Regards, Marc

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