[mkgmap-dev] Coastline issues - analysis and possible solution

Mon Aug 29 07:16:59 BST 2011

On Mon, Aug 29, 2011 at 08:07:04AM +0200, michael lohr wrote:
>My feeling with the problem of flooded tiles always was that the 
>geofabrik extracts are to blame - they're too "tight" in some places, 
>so the coastline breaks in the extraction process already, not during 
>the splitting. That happens for instance in the northwest of germany 
>around emden and in the northwest of india in gujarat.

The Geofabrik cutting polycons are not set in stone. A long time ago, I 
took a couple of iterations with Frederik Ramm to get a good extract of 
Finland that would include all of the country border, plus some lake 
multipolygons in the neighbour countries. I did this in Osmosis and JOSM 
by extracting the country borders from the Geofabrik extract and by 
downloading some data in JOSM, and finally editing the cutting polygon 
in a separate JOSM layer.

It still takes a little tweaking to get the coastlines right. I have 
manually chosen the tile borders so that the coastline will end outside 
the tile border. Only in the Swedish/Finnish border I am using 
extend-sea-sectors to make up some coastline in Sweden.

I think that it could be useful to have the tile-splitter support a set 
of fixed tiles that it would split itself further as needed.

Best regards,

	Marko