[OSM-talk] Key:layer update
ricoz.osm at gmail.com
Sun Mar 9 10:30:47 UTC 2014
for some time now I have been working on the wiki page to state the rules
as clearly as possible.. hope that most of the improvements are fairly
uncontroversial. Some of the changes:
* the vertical ordering established by the layer values is valid exactly only
in the point where the ways cross or objects overlap
* define layer as higher value means above, lower value means bellow. Avoid
the complicated layer=0 definition as "the natural ground level as it
would be shown by contour lines on a topographic map". Explicit layer=0
seems to be deprecated now.
* layer on ways should be used only in combination with one of tunnel=*, bridge=*,
highway=steps, highway=elevator, covered=* or indoor=yes. For areas, it could
be used in combination with tags such as man_made=bridge, building=* and similar.
The motivation for this is to make it easy for validators to spot errors such
as when the wrong segment is accidentaly tagged, bridge/tunnel forgotten, or
someone tags excessively long ways for no good reason - common problem with
waterways and elevated roads/railroads.
I have validated this rule for ways in large parts of the world, there are
exceptions which currently I do not know hot to tag better but those are rare.
* in some cases "level" may be more appropriate than "layer"
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