[OSM-talk] area topology

[Ulf Mehlig]

Please excuse me if this is a FAQ, I just didn't find an answer in the
wiki (possibly because it is obvious) ... 

In topological GISses like grass, borders are shared between adjacent
(vector) areas. However, I wonder how adjacent areas should be digitized
in OSM (let's say, forests and farmland, or riverbanks and the
associated wetlands). Am I right in assuming that OSM ways always belong
to one single area? If this is so, do I have to duplicate ways along the
common border? JOSM informs about double ways when it validates data so
I had the slight impression that they are not really wanted.

I see a similar problem with line data (e.g. roads, streams) which may
happen to be an area border. From reading

http://wiki.openstreetmap.org/index.php/Editing_Standards_and_Conventions#Tagging_Areas

I think that using a street as a border of a plaza (or a block of
buildings) is not wanted. Does one digitize double ways, leading along
the same nodes, or does one make a separate area in a small distance to
the existing line (street/stream), which might be topologically
incorrect and is more difficult to maintain?

Thanks for your advice!
Ulf

-- 
 Ulf Mehlig    <ulf.mehlig at gmx.net>
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