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Summary When all is said and done, I don't believe there is an agreed upon method of combining (or prioritizing) the place=* and boundary=administrative tagging schemas for populated places (e.g., counties and cities). If there is, please feel free to point me to the relevant writeup - or try answering my questions below. In detail I have been reading and rereading pages on Place key and Boundary relation, and I feel we have talked about it here a lot but I am still confused. Looking up the actual tagging on the ground just adds to my confusion because various user communities do it differently. How are we supposed to tag an area where the border 1)is the same for the settlement and the administrative area and 2)is shared by two neighboring entities? It seems to me that if I don't want to end up with redundant ways, the only way to tag is using the boundary schema, where each segment segment belongs to a minimum of one and a maximum of two boundary relations. And if that is the case, shouldn't the boundary/multipolygon schema be preferred over the place=* schema for all cases when the admin border and settlement boundary coincide? And if that's true, then how far away are we from saying that the place=* schema should be applied to nodes only and boundary schema should be applied to polygons? The As areas portion of the Place key wiki page seems to come close to recommending just that, but it can be interpreted as saying we should be applying place=* tags to settlement boundaries that do not coincide with admin areas. |
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I am going to state what transpired in our little conversation as an answer for posterity. The answer also includes bits and pieces of advice I received elsewhere, so feel free to comment if you consider some of it incorrect.
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This answer is marked "community wiki".
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2) In some countries, an area enclosed by an administrative area boundary can contain more than one settlement. That's why the two tagging concepts exist and are complementary. 3/4) I don't know why the purists would require duplicate relations with identical sets of members. It certainly isn't necessary as far as OSM itself is concerned. 5) I once tried to slightly modify the wiki to favour multipolygon relations for boundaries, while not at all deprecating type=boundary flat out. Those strong opinions you mentioned caused others to quickly revert my edit.
(22 Apr '11, 20:17)
Lennard
2)Absolutely. But my quest has always been to determine which tags should be used in a country where they are the same. 3/4)I can take the mention of the purists out if that could confuse anyone and sounds outlandish.
(22 Apr '11, 20:25)
ponzu
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IMHO there is a clear distinction between the two, which might overlap in certain cases. Place has nothing to do with administrative boundaries, it is dealing with the topography of settlements. On the other hand, administrative boundaries are only about legal (administrative) limits, they don't deal with the actual built up space. Forgive me for marking your answer down: it is to indicate that I don't consider my question answered. Nothing personal, I know you want to help. I keep hearing this opinion, so it's not just yours (or else you keep answering my questions on this topic), but it just happens to be that where I live there is no distinction between a settlement and legal limits. The topography is defined by the administrative boundaries. Where one city ends, the next begins, with houses on each side of the street delineating the two "settlements", and residents often confused which city their are in.
(20 Apr '11, 22:49)
ponzu
This may be unusual and hard for the rest of the world to picture, but this is how we live. About 20 million people, give or take.
(20 Apr '11, 22:53)
ponzu
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no, there is no problem with this, in your case both do coincide. But you should be aware that this is not the same everywhere, that's why there are two tags for it.
(20 Apr '11, 22:56)
dieterdreist
Agreed, so that means that the answer to the third (and possibly second) part of my question may be "no". Now I just need to figure out the first part. I actually got an interesting suggestion from someone elsewhere: map out the cities as multipolygons and tag the multipolygons as both administrative and place=city. I am happy to go that route if that's an accepted convention. So far everything I have read says to only tag closed ways as places and multipolygons as administrative.
(20 Apr '11, 23:10)
ponzu
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Closed ways and multipolygons, conceptually, are the same. They are as related as a square and a rectangle are. A closed way is an area with no bells and whistles possible, and a multipolygon is also an area, but with the possibility of holes (and multiple outer rings, if you ask some).
(21 Apr '11, 21:15)
Lennard
So - to finish your thought - it is perfectly correct to tag a multipolygon with place=*, and it is also correct to tag the same multipolygon with place=* and boundary=administrative + admin_level=* if the administrative boundary coincides with the settlement? Both schemas are in use, they are parallel and non-exclusive? Am I finally getting it? And maybe it is even okay to tag a closed way with boundary=administrative? Or is that taking it too far? If you're saying that closed ways and multipolygons are the same, then there should be no restrictions on tagging either way.
(21 Apr '11, 21:50)
ponzu
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@Lennard: a closed way might describe an area, but also not. Multipolygons do in all cases describe areas. A closed way might just as well be a linear object. This depends only on the associated tags and on interpretation (even more if there is no tag area=yes/no).
(22 Apr '11, 10:14)
dieterdreist
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@ponzu: Yes to all your questions except the "taking it too far" one. @dieterdreist: Thank you for pointing out that some closed ways do not describe areas. I should've mentioned that there are exceptions and as you say: the tags make the difference. I was only thinking about the most common closed ways (landuse, administrative regions, etc) and the example at hand. For these examples (place tagging and administrative areas), a closed way would describe an area.
(22 Apr '11, 10:30)
Lennard
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