[mkgmap-dev] inner sections of a multipolygon

Mon Aug 1 12:09:38 BST 2016

2016-08-01 13:56 GMT+03:00 nwillink wrote:
> Once you add a multipolygon relation to say an existing forest and making it
> outer, any inner sections created don't show up unless :
>
> the landuse=forest gets removed from the polygon and added to the relation.

  This is how multipolygons should be tagged in OSM - forest tags
should go to relation, not to outer polygon.

  Outer polygon is a different geometry compared to multipolygon
(polygon with "holes"). For example, lets say you have a park which is
mostly trees, but in the middle you have a meadow/grass. You would
then have 3 objects:
  1. outer polygon which would be tagged as "park" (because park
contains both forest as well as meadow)
  2. inner polygon which would be tagged as "meadow"
  3. relation which is tagged as forest, because forest is everything
inside outer polygon except inner meadow polygon.
  Note different geometries for park and forest. Only relation
represents a geometry with a "hole".

P.S. JOSM validator reports such errors. I'm not aware of any other
validator doing that.

-- 
Tomas