[mkgmap-dev] Handling of Multipolygons in Tile Splitter

Mon Aug 15 09:23:29 BST 2011

On Sun, Aug 14, 2011 at 10:13:36PM +0200, Wolfgang Hammel wrote:
>Im not sure wether tile splitter did some processing in order to close 
>the multipolygon along the bounding box, but probably this ist not the 
>case.

It does not. This is a known problem in the tile splitter. mkgmap does 
try to work it around to the extent possible.

For what it is worth, the splitter in Osmosis implements an option not 
to break relations (such as multipolygons). It costs much more 
processing time.

I do not know how much additional effort it would take to clip 
multi-polygons (and polygons, for that matter) along tile borders in 
splitter.

>As I already mentioned, this large multipolygon is no more present in 
>the actual osm database.

There are some large multipolygons elsewhere on the planet. One example 
is Lake Päijänne in Finland. The largest lake, Saimaa, is in several 
multipolygons, and every now and then someone adds an island to the 
wrong multipolygon relation.

Best regards,

	Marko