As you said it yourself, a different example. As for national parks, everything inside its borders belongs to the park. Unless it is explicitly excluded by some inner (hole :) ) borders. Same goes with the country borders. I think there are quite a few examples of chunks of a country A's territory totally surrounded by country B (see http://en.wikipedia.org/wiki/Exclave). And you wouldn't calculate the area of the country B including those chunks. That's why multipolygon holes are not a bad idea.
As far as I know, when calculating surface area of a lake, only the water-covered areas are taken into account (but since I'm no expert in these matters, correct me if I'm wrong). So lake islands should not be included (that's where the multipolygon holes come nicely). On the other hand, if you had a permanently docked museum ship on that lake, it would not be defined as a hole, but as a polygon with layer=1 and that would be ignored (/included) in the area calculation. Igor On Tue, Mar 4, 2008 at 10:21 AM, Martijn van Oosterhout <[EMAIL PROTECTED]> wrote: > On Tue, Mar 4, 2008 at 7:37 AM, Igor Brejc <[EMAIL PROTECTED]> wrote: > > That's fine if you look at OSM data from the presentation viewpoint > > only. But what if sometime in the future somebody wanted to calculate > > its surface area? ;) > > Are you saying that if someone asks you to calculate the area of a > national park, that they're expecting you to subtract the areas of any > lakes, ponds, rivers within it? Different example, but you get the > idea. > > The area of a housing estate includes the area of the buildings on it. > > If there is a forest with a lake in it and I get on a boat, have I > left the forest? I'd say no (you are simultaneously in the forest and > on the lake), but I can imagine people disagreeing with that. My point > is that the question "What is the area of feature X" is too weakly > defined to be basing our structure on the answer. > > Have a nice day, > -- > Martijn van Oosterhout <[EMAIL PROTECTED]> http://svana.org/kleptog/ >
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