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> On 17. Apr 2019, at 01:48, Joseph Eisenberg <joseph.eisenb...@gmail.com> > wrote: > > Yes, that’s my recommendation. You just need a tag that is for groups of > lakes. multipolygon relations have different semantics, they “combine” the parts while the group is about an ensemble. With the group relation you do not “just need” a tag for groups of lakes, trees, stones, sculptures, summits, and any other group of things. > > Archipelagos are mapped as multipolygon relations tagged with > place=archipelago, name= and type=multipolygon. This makes it easy to search > for, does not duplicate the place=island tags on each island, and can be > rendered with existing tools. and doesn’t work for islands mapped as nodes. I agree that place=archipelago has a well defined meaning and helps to better understand what the object is about, especially those represented with a multipolygon relation, where it isn’t clear from the members what kind of thing the whole is. > > A named group of lakes is similar to a water equivalent of an archipelago > (especially if they are not connected by rivers) all groups of things are similar in this regard. The most meaningful property (the reason people would usually want to create an explicit relation between the parts, on top of the already existing implicit relation through proximity), is a common name that wo/mankind has given to it. For rendering support (or search / geocoding support), the group relation would probably depend on osm2pgsql supporting it. Derivative auxiliary geometry (and ontology, possibly size information) would be created in the osm2pgsql step, so the rendering team would not have to walk down the list of members to guess the domain of the thing, where it is or how big it is. For humans looking at the data, a group of trees, lakes, dunes, tombs or sculptures will be easily understandable, computers may have a harder time but would usually not need to „understand“ it, for most applications a rough idea of the domain (e.g. key level meaning like “historic”, “natural”) and extent is all they actually need to know. Cheers, Martin
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