[OSM-dev] Looking for guidance on interpreting multipolygon relations

[Maarten Deen]

Frederik Ramm wrote:

>> As a side note, can someone explain what a multipolygon is good for and 
>> in what circumstances you would want to use it?
> 
> It is used for areas with holes in them. 

That is a bit terse. With an explanation like that I still don't know 
what it is good for (and judging from what I see on the map I'm not the 
only one). But Bart mailed me a good example which I think should be 
added to the wiki page about mulipolygon.

Some observations:
1) it should not be applied to ways, only to areas?
2) it should not be used to single areas that are contiguous?

ex 1): I've seen multiploygons tying the left and right way of a 
motorway together, I assume that's false.
ex 2): I've seen multipolygons applied to a natural=water where a lot of 
ways were double and they were connected with a multipolygon (making the 
T&H renderer do silly things)

Additionaly, the discusstion Bart started needs to go on the wiki page, 
because those are exacly my questions now I know what it is good for.

Maarten