[Talk-us] Landuse polygons within landuse polygons

stevea steveaOSM at softworkers.com
Mon Feb 11 23:07:45 GMT 2013


(While both are important, I begin this thread In the interests of 
taking this list out of the OSM social and more into the OSM 
technical/practical):

I have questions about landuse polygons.  For example, barracks, 
where soldiers are quartered (housed) inside of a military base.  A 
polygon surrounding the military base (where the boundary is) with 
the tag landuse=military seems correct, indeed there are many 
examples.  For the barracks specifically, do I draw the buildings and 
tag them building=residential?  Sure, that seems correct, too.

But, do I also add a polygon with landuse=residential to the "zone" 
or "neighborhood" where the barracks are clustered?  This would be a 
double-overlap of landuse polygons, residential "on top of" or 
"within" military.  Sure, I could make the landuse=military a 
multipolygon  (outer member) and punch a hole in it with the barracks 
neighborhood as an inner polygon, but in so doing we lose the 
semantic that barracks are BOTH military AND housing.  At the same 
time, we don't want to approach or achieve coding for the renderer.

Similar questions arise with "other" (non-landuse) tags which might 
logically be applied "over" one another.  An example is a (say, 
largely wooded) leisure=park polygon with several landuse=meadow 
polygons sprinkled about it.  In this case, leisure and landuse ARE 
distinct tags, so no double-overlap is strictly happening.  And in 
mapnik, the effect is rather pleasing.  (See, for example, 
http://www.openstreetmap.org/?lat=36.98499083518982&lon=-122.0841121673584&zoom=15).

In a nearby case, a leisure=park is so largely wooded that a 
natural=wood tag is ALSO applied to the entire park multipolygon, but 
there are also some landuse=meadow polygons sprinkled about.  Here, 
we have three different polygon tags:  leisure, landuse and natural. 
Mapnik handles this well, again with a pleasing effect 
(http://www.openstreetmap.org/?lat=36.98982&lon=-122.11378&zoom=17&layers=M).

While these parks (woods, meadows) "look good" in mapnik, are such 
superimposed polygons the correct representation in the underlying 
OSM data?

Is the correct answer to never double-overlap landuse (or any 
like-tagged) polygons, but to use multipolygons with inner members? 
What about where the semantics really include "both," like barracks?

Thanks for an enlightened discussion about superimposed polygons 
(with both same and different tags),

SteveA
California



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