[Tagging] Layer=* tags disappearing

[Nathan Edgars II]

On Tue, Oct 12, 2010 at 12:04 PM, Colin Smale <colin.smale at xs4all.nl> wrote:
> What layer is the road on which connects the rest of the road network at
> ground level (layer=0) to the bridge itself (layer=n>0)? I seem to remember
> a discussion about joining ways on different layers..can't remember the full
> conclusion but I believe it was that the layer tag is only for rendering
> purposes and doesn't imply anything reliably about above/below.

If the road's on an embankment until it reaches the bridge, it's still
on the (artificially-raised) ground and hence (implied) layer=0. If
anything passes under the embankment it's either a short separate
bridge or a tunnel (there's no clear line between the two).

Two ways on different layers should not cross, and one could argue
that if a node has more than two ways all should be the same layer.
But there's no way to avoid a change in layers along a way (such as in
a trefoil knot).