[OSM-talk] Mulltipolygons and Mapnik

[Cartinus]

On Friday 23 May 2008 21:18:40 Ludwig wrote:
>    - Land that exists within another area, such as a lake. (i.e an island).
>    Keep water on the right and land on the left side in relation to
> sequence of nodes in the Way. Layering may also be required. See
>  
>  Relations/Multipolygon<http://wiki.openstreetmap.org/index.php/Relations/M
>ultipolygon>for islands in lakes

You either hack around with natural=land and layers (which is bad practice 
IMHO) or you use multipolygons. Trying to do both at once is just weird (and 
not really what that text is trying to say.)

- - - - - - - - 

After the last round of discussions about how to tag multipolygons I left some 
tagged in different ways around my home city. I just checked the current 
state of their renders.

1)
outer tagged with feature X & inner tagged with feature X
- Works with osm2pgsql used on the main site (i.e. the mapnik layer)
- Works with Osmarender

2)
outer tagged with feature X & inner not tagged at all
- Does not work with osm2pgsql used on the main site (i.e. the mapnik layer)
- Works with Osmarender

3)
outer tagged with feature X & inner tagged with feature Y
- Does not work with osm2pgsql used on the main site (i.e. the mapnik layer)
- Does not work with Osmarender

So your first example doesn't show the islands because they are not having 
tags. I don't know why the island in the second example doesn't work. The 
relation and both the inner and outer polygon look OK.

-- 
m.v.g.,
Cartinus