pulling this from dev to tagging
2013/2/11 Christoph Hormann <[email protected]>: > You might notice various strange forms in the coastline at some places, > most of them are caused by features being tagged as coastline which in > fact should probably not be. I put up a wiki page [5] to collect these > problems. If you find more or fix them feel free to edit that. > [5] > http://wiki.openstreetmap.org/wiki/User:Imagico/coastline_problems_for_generalization I had a look on the examples, the first one is the Suez canal. What I found strange is that the southern part is closed while the northern isn't (i.e. in the south there would be an overlapping coastline, which probably shouldn't occur). But: it is an open (i.e. there are no locks) connection between the Mediterranean Sea and the Red Sea with saline water. It is not a natural feature, ok, but isn't it still a coastline? This is also an example for a common problem: there are 2 relations where this way belongs to: http://www.openstreetmap.org/browse/way/97208606 // has no meaningful tags http://www.openstreetmap.org/browse/relation/1410016 // with the following tags: is_in = Egypt, جمهورية مصر العربية various name tags (name:en = Great Bitter Lake) natural = water type = multipolygon 3 redundant (because interlinked) language-specific wikipedia tags http://www.openstreetmap.org/browse/relation/1211874 // has no tags which really tell what this is: boat = yes // attribute man_made = yes // attribute name = Suez Canal // probably not the local language, but that's not my point here various other name tags type = canal // undocumented relation type shouldn't there be some tag to say what kind of object this second relation is, e.g. natural=water or natural=coastline or waterway=riverbank? But then you would get 2 overlapping water areas because also the other relation (above) has a natural=water tag (maybe this is not a problem?). I don't think you can safely asume that this relation inherits the kind of object from one of its members. This kind of problem also occurs in other contexts, e.g. a forest with a name which is part of a bigger forest (with a different name). Currently as far as I have seen this on the map there is mostly tagging for the renderer (one object only gets the name, while the other gets the forest-tag and the name). But this way you don't know what kind of object is the one with just the name. This could be resolved if we had a clear distinction of physical objects and logical objects, e.g. a tag that says: this is a "forest" and it has the name foo, this is another forest and it has the name bar (and foo and bar could well overlap), while you would have another tag that says: here are growing trees (because you cannot asume that inside the polygon that is commonly called "forest foo" there will be trees everywhere, e.g. there could be a lake in the forest, and still this lake could be considered "in the forest, part of the forest" so excluding it with a multipolygon inner role from the logical (named) forest would be wrong). In my interpretation, the named, logical object forest would be tagged with the key "natural" while the second object (here trees) could be landcover. cheers, Martin _______________________________________________ Tagging mailing list [email protected] http://lists.openstreetmap.org/listinfo/tagging
