The OSM renderer does not show buildings which are made of several ways with a relation(type:multipolygon, building:yes):outer.
You can usually expect applications to handle multipolygon relations with one closed way outer member and closed way inner members that don’t intersect with each other or the outer boundary (which is how multipolygons used to be defined). Almost no application fully supports “advanced” multipolygons - which isn’t surprising because they are, in my opinion, unnecessarily complicated constructs.
Personally, I suggest avoiding non-closed ways as multipolygon members for everything except extremely large objects (such as borders) that cannot be split into independent areas.
It would still be nice to have at least one reference renderer which is fully compatiple to the mapping standards.
The “OSM renderer”, by which I presume you mean mapnik, has no problems drawing multipolygon relations where the outer ring is made up with more than 1 way. In fact, if you want to get technical, it’s the import tool osm2pgsql which constructs the geometries that mapnik will draw, but that’s just a technicality.
It would be most helpful if you showed examples of where this does not work, according to you.
@Tordanik: you have ‘advanced’ multipolygons, and then you have ‘advanced’ multipolygons. There as so many variations on the wiki page, that it’s always good to be explicit about the exact type we’re talking about. Personally, I have no issue understanding and using them. They’re powerful, and not hard to understand.
sorry for the late reply.
As example you can look at relation 416760 (building Afrikahaus) in
I could not find any reason, why everything is redered ok - but not the building.
I’m not sure, but I think, when some parts of a mutlipolygon are clockwise and an other part counterclockwise, the renderers will have a problem. Try to adjust the ways all in the same way…
In that case you will never find an adjustment, where all areas are correct in one direction - so the whole idea of advanced multipolygones would be nonsense. It works pretty well for other area types - so why not for buildings?
On reason can be that Africahouse seem to have a typo and relation is of type “multipoygon”.
Sorry but your usage of advanced multipolygons is horrible IMHO.
A new user will never understand the zoo in an editor (potlatch/JOSM)
It’s the best to use simple areas and use advanced multipolygons only if you need them.
A good reason whould be areas with many nodes like the bodensee.
The problem with simple areas is that you have no chance to get a proper rendering result, if you have areas in a zoo in a park and only one border line (inner and outer nomal polygon can not touch). In fact, in an editor it does not look nice - but it works. Editors may be improved to show advanced multipolygon areas.
My zoo example was just a test to avoid long overlapping ways.
I look forward to your patch.
Showing advanced multipolygons would help advanced user like me to understand the areas faster but that will not help new users to understand relations.
Relations are easy if you understood them once but I think 75% of all OSM users don’t know how to use them.
You can do everything with normal areas except if you hot the node limit.