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I have seen a couple of these multipolygon relations to create fairly simple shapes. Is there any good reason for making a rectangular building by making the 4 walls separately then creating a relationship for them as a building? I find it makes them harder to edit and don't see any benefit. Is there any problem with a node having more than one way go through it? |
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There is no good reason for mapping a simple building as a multipolygon with separate ways for each wall. Ideally, you should talk to the mapper who did this, and if he doesn't come forth with any unexpectedly good explanation, these buildings should be turned into a single closed way each. In general, multipolygons for areas without holes should only be used for very large areas, and no building comes even close to that. Not even when an adjacent area runs right up a wall of the building (eg. a parking lot or another attached building)? Are you saying it's recommended to have overlapping ways rather than using multipolygons to share the way? If not, what's the recommended solution for such a scenario?
(27 Mar '14, 16:27)
alester
Overlapping ways are a perfectly valid approach of modelling adjacent features. It's semantically equivalent to using a multipolygon and much easier for inexperienced users to work with.
(27 Mar '14, 16:35)
Tordanik
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Hi, well I think this question mixes two slightly different things:
Multipolygones allow you to model more complex shapes as you would be able just with a single closed way. This includes esp. shapes with holes or shapes with 2 completely seperated bodys. Using MPs you can keep the semantics clear ("this is one single object") or don't need to fake the geometries (e.g. keeping a fine line that avoids a full closed hole in a doublebox shape).
Buildings aren't different here, but the Simple 3D buildings schema enforces a relation (but not to glue all the walls together). Also some indoor mapping schemas might make use of this very fine grade of modelling (as you can tag walls seperately). AFAIK this wall based modelling isn't common sense yet. We are talking about a multipolygon relation, not a building relation, so neither Simple 3D Buildings nor indoor mapping should be relevant here.
(27 Mar '14, 11:30)
Tordanik
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