Our German colleagues have just proposed a new method for tagging boundaries / borders. I'll quote them here and direct you to find the original thread on talk for comment and discussion.
First an email from Frederik, then one from Jochen. They both relate to borders and maritime borders. Best regards, Richard Subject: [OSM-talk] Using multipolygons as boundaries From: "Frederik Ramm" <[email protected]> Date: Sun, January 4, 2009 4:08 pm Hi, those of us who use relations to tag administrative boundaries usually apply the schema described in http://wiki.openstreetmap.org/wiki/Relation:boundary which suggests to use a type=boundary relation with "enclaves" and "exclaves". At the time of conception, that was ok because administrative areas (e.g. countries) often required border lines taht consisted of many ways and exclaves, something that plain multipolygons did not support. Since we now have "advanced multipolygons" as described here: http://wiki.openstreetmap.org/wiki/Talk:Relation:multipolygon#Advanced_multipolygons (which, being true to their name, support any number of disjunct areas which may have zero or more holes each, and even islands in holes and so on), there is an equivalence between the two: each administrative area corresponds to exactly one multipolygon. I am thus suggesting that we drop using the special "type=boundary" relation and instead use a simple "type=multipolygon" for administrative areas. Everything else would stay the same (boundary=administrative, admin_level=x, name=y, ...). Members would not carry the roles "exclave" and "enclave" (which seem to have been difficult to understand for some), but instead simply "outer" and "inner" just like with plain multipolygons. I have described the suggested change in detail here: http://wiki.openstreetmap.org/wiki/Talk:Relation:boundary#Use_type.3Dmultipolygon_instead The main advantage of this is that any piece of software that works with our data would just have to understand multipolygons - wheter they are additionally tagged as representing a boundary, a forest, a lake or whatever - instead of having to carry a list of relation types that form one or the other kind of area. Bye Frederik -- Frederik Ramm ## eMail [email protected] ## N49°00'09" E008°23'33" Subject: [OSM-talk] Comprehensive proposal for tagging of boundaries From: "Jochen Topf" <[email protected]> Date: Sun, January 4, 2009 5:47 pm To: "Gustav Foseid" <[email protected]> Cc: "osm" <[email protected]> Priority: Normal Options: View Full Header | View Printable Version On Tue, Dec 30, 2008 at 10:32:45PM +0100, Gustav Foseid wrote: > I would suggest that maritime borders are not tagged the same way as land > borders. Should we have a new tag for maritime borders? Stop tagging them? > Ignore the problem? We had the same discussion on the talk-de mailing list. There are several things here: a) We should move away from tagging the ways of the boundaries with all sorts of stuff and move this information into relations. This is much cleaner and allows different kinds of borders to co-exist on the same ways. b) Some people need borders on the water, the "official" borders of whatever entity we are talking about. Others would prefer to use the coastline as boundary. Clearly there is a need for both. So here is the proposal for how to tag things: (This also ties in with Frederiks post about type=multipolygon vs. type=boundary.) All boundaries are made up out of ways. Those ways are tagged with boundary=administrative. Where the boundaries go out on the water, the ways go out on the water and are still tagged with boundary=administrative. All ways belonging to the boundary of some entity are put together into a relation tagged with type=multipolygon boundary=administrative admin_level=<something> This includes the ways going out into the water. Boundary ways are shared between several levels of administration. So if a border is a country border and at the same time a state border, the way is in two relations, one for each. Exclaves and enclaves can be modelled with the multipolygon relation without any problems. (See Frederiks post for details.) If there are several relations on the same ways, the admin_level for those ways is the one with the smallest number (ie. the highest administrative level). This is redundant, but it allows renderers to ignore the relations for many cases and just render the ways. Borders will show up as they should with more important borders drawn instead of less important ones. There is a second relation for every administrative entity. It contains all the boundary ways on land plus the coastline connecting those points where the boundary crosses into water. So it is the land area of this administrative entity. It is tagged as type=multipolygon land_area=administrative admin_level=<something> So if you are interested not in the boundary on the water, but just want the land area, you use this relation. For entities that are completely on land only one relation is used and it is tagged with both: boundary=administrative land_area=administrative In the land_area relation islands will show up as seperate areas. But they are still in the same multipolygon relation. Note that this proposal only gives you a way how to tag maritime boundaries and have the land area, too. It does not say where those boundaries are supposed to be and whether one or the other makes more sense, thats a different discussion. This proposal is mostly backwards compatible with existing use. If existing borders are on the coastline, they can stay there until somebody wants to change it. Relations have to be added in those cases, where they are missing. Some existing relations will get extra land_area tags, some new relations for land_area will be created. The biggest change is from type=boundary to type=multipolygon, but see Frederiks post for that. Jochen -- Jochen Topf [email protected] http://www.remote.org/jochen/ +49-721-388298 _______________________________________________ Talk-ca mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk-ca
