[OSM-talk] Changed highway=*_link meaning?!

[David Paleino]

On Fri, 25 Jun 2010 06:10:18 +0000 (UTC), Ed Avis wrote:

> John Smith <deltafoxtrot256 <at> gmail.com> writes:
> 
> >>and uphill/downhill for slopes (based on the layer of the endpoints).
> > 
> >Layer has nothing to do with elevation, it only indicates which road
> >goes over the other road there may not be any slope involved.
> 
> True, but if a way is tagged highway=steps or slope=yes, it's a pretty safe
> bet that going from layer 0 to 1 is uphill, and 1 to 0 is downhill.  Even
> though in theory there is nothing to guarantee that. 

Not only theory.
Suppose you have a downhill highway=steps intersecting some other thing below.
It's up to the mapper whether to tag this "thing" layer=-1 or to break the
highway=steps and tag the middle segment layer=1. With your example, instead of
the reality, you'd be ending up with an up followed by a down.

layer=* is just really for the rendering, and shouldn't be used for anything
else.

> (And if elevation is tagged, uphill and downhill markers can be deduced for certain.)

Yes, that is the only safe tag.

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