On Tue, Oct 2, 2018 at 12:03 PM Paul Allen <pla16...@gmail.com> wrote: > Even if a multipolygon can have many disconnected outers, it seems I'd have > to make each university > building an outer. And then there are no inners. So even if it can be done > that way, it seems like > an abuse of the concept, which I thought was to be able to punch exclusionary > holes in areas.
The one that I pointed you at has a great many disconnected outers. It's called a MULTIpolygon precisely because it can represent multiple polygons. Most GIS software calls your idea of a multipolygon simply a 'polygon', and the OSM concept of a 'closed way' is a 'ring'. Hence, in ordinary GIS terminology, a 'ring' must be a simple closed region, a 'polygon' has an outer ring and zero or more inner rings, and a 'multipolygon' may have multiple outer rings. If mapping a complex area like https://www.openstreetmap.org/relation/6360587 as a multipolygon with disconnected outer rings is an 'abuse of the concept', that's news to me - and I'd really like to know what the accepted concept for how to map those is, because I've mapped hundreds of cases like it (well. all right, it's an outlier at the high end of complexity, but I'm sure that I've got hundreds of multipolygons with disconnected components). I don't see adding the lot of an isolated building to a multipolygon as being any more difficult than adding it to a site. If the university's holding is an office or floor, represented by a node in OSM, in addition to land area elsewhere, that might be a call for a different type of relation, since only ways make sense as components of a multipolygon. If 'site' is the correct description of that, so be it. I haven't yet confronted mapping that particular sort of beast, but I concede that I can see wanting to map, "the university comprises this lot of buildings and grounds, as well as operating out of these offices and storefronts' - and a multipoygon can't do that. Still, in any case, when a particular region or facility comprises disconnected parcels of land, a multipolygon with disjoint outer rings is a natural way to map it, and all the tools cope with that topology quite well indeed. _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging
