[mkgmap-dev] How to tag artificial cut lines in multipolygons

Wed Feb 17 20:23:48 GMT 2010

Hi WanMil and others,

Some time ago, there was discussion that the MultiPolygon code in  
mkgmap should tag the lines that it generates when splitting  
multipolygons to polygons.

I think that there is a genuine need to split large multipolygons to  
smaller multipolygons in the OSM data too. For example, I generated  
multipolygons for the lake Saimaa in the past couple of weeks. I split  
it to maybe 10 or 20 multipolygons, some of them still huge (hundreds  
of ways in the relation, many of them consisting of 500 nodes).

A fellow mapper who generated the natural=coastline for many Finnish  
waters in the first place got upset of the artificial splitting. I  
suggested a solution where the artificial split lines would not be  
given any natural=water or natural=coastline tag, but something else,  
say, artificial=yes.

What do you think? Is there an existing tag that we could use for this?

Is there now a multipolygon around the Canarian Islands? I could not  
find one. I am considering defining some multipolygons with some  
artificial cut lines on the Finnish coast, so that I would get water  
without --generate-sea and could work around the limitations of the  
Geofabrik map extracts by defining the borders of the sea multipolygons  
within the Geofabrik cutting boundary.

	Marko