On Jun 21, 2020, at 5:58 PM, Mike Thompson <miketh...@gmail.com> wrote: > 1) Not all "inholdings" are completely surrounded by the National Forest, > they are "bites" off the edge in some cases. I don't think one can have an > inner ring and an outer ring which are at all coincident (they can't share an > edge) and still have a valid multipolygon.
I don't wish to sound dismissive as it seems we largely agree, but this is merely quibbling over constructing an outer edge. If truly a "bite off the edge," then it seems the outer polygon should shrink to accommodate, no need for edge mumbo-jumbo (though sometimes these edge memberships take on a tagging life of their own and it gets to be a high-wire act as to how "loaded with tags" each one might become). There are a lot of methods to capture semantics using syntax that is crisp and unambiguous, I believe some methods are smarter (less or even no ambiguity about the semantics that are "meant") and cleaner (fewer data) than others. There is what might be characterized as "a wide zoo of tagging in these realms" (nationally at the enormous polygon scope). Thank you (again) to Kevin for the word "menagerie" here. This also enters what some have dubbed "higher math" (multipolygon edge tagging in a relational database and how deep these semantics can be relied upon are a "topology of deep genus"). > 2) Holes (inner rings) are not part of the polygon. Thus if one did an > analysis of (for example) a series of points, any points that fall in one of > the holes would not register as being inside the multipolygon, even though > they are inside the outer ring. That sounds right. And a snappy-efficient way to achieve what is "truly excluded as PRIVATE" as an inner member of an "outer polygon that describes geographic extents of this PUBLIC forest" is by simply tagging what IS the inner member with "what it is." That might seem fancy word salad, so I want to break down what we say as understandable to both of us. We're using the double-duty that in a public forest (with a large, enclosing geography, but no larger than necessary or truly) which is tagged as outer role, anything we tag inner role is EXCLUDED from the public forest. That "inholding," in every sense I've ever seen it, is private, hence, it's an inner to the outer, as private isn't public and vice versa. The logic of opposites, the power of roles (inner and outer) in a relational database and the geography (in 2-space) of what we "mean" (quite intentionally) by inner and outer become powerful. Let's simply tag the "thing inside, different from its enclosing polygon and so excluded from that polygon" for what it is, then include it as an inner member of the relation. We do this, the logic of "nodes registering or not" is already built into "the space." Think of a grassland in otherwise-land-filled-with-trees, it's a (mathematical) "hole" (of the 2-space, lat-long of nodes OSM lives in). It simply works, like math, geography, software. (Um, "well written" software!) Meet you off list? Steve _______________________________________________ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
