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

Bryce Nesbitt bryce2 at obviously.com
Wed Apr 2 06:21:51 UTC 2014

The present situation is that rivers implicitly render below highways in
all common renderings.  That's not necessarily bad. With some formality to
the layering arrangement, it sure would save a lot of tagging hassle and

The new cloud tag for example, is clearly to be rendered after everything
but the celestial tags.

April 1st aside: the number of important implicit assumptions is relatively
small.  Rivers under, power lines over, closed ways under except if they're
tagged building, etc.  Currently this type of layering is implicit in
various bits rendering software, but
it could be formalized at the tag definition level to help meet certain
mapper expectations.

In the case of the river/highway layer warning: if the warning had never
existed, chances are the various workaround schemes would never have come
up.  Rivers would run under roadways, and tagging would be needed only in
the rare case of a ford or an arroyo with no culvert.
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