[mkgmap-dev] Flooding in Southern Scotland

Fri Dec 30 20:52:49 GMT 2011

On Fri, Dec 30, 2011 at 08:01:42PM +0000, Roger Calvert wrote:
>I have today downloaded new files for Scotland and England (and Wales)
>from Geofabrik, and I still get extensive sea flooding in NW England 
>and SW Scotland. I have examined the coastlines in the area in as much 
>detail as I can (using Potlatch 2 and Geofabrik Tools) and can't find 
>any problems.

Did you enable logging in mkgmap? Do you see any coastline related 
messages in mkgmap.log.*?

One thing that you could try is to extract the natural=coastline ways 
from the Geofabrik extract that you are using, loading that in JOSM and 
having Validator check it.

Sometimes, mkgmap remains silent about flooding. A few months ago, there 
was an island in a lake in SE Finland drawn as natural=coastline.  
mkgmap did what it was told to, and flooded the whole map tile except 
for the tiny island, because there were no other natural=coastline ways 
in the tile. mkgmap could perhaps have done a better job and complain 
that some natural=water polygons or multipolygons are overlapping with 
the natural=coastline multipolygon. This error I fixed by looking at the 
natural=coastline extract in JOSM.

The commands go something like this:

osmosis --rb xxx.osm.pbf --tf accept-ways natural=coastline \
--tf reject-relations --used-node --wx coastline.osm
josm coastline.osm
[invoke the Validator in JOSM, and be sure to enable INFO level in the 
preferences, because coastline checks are in the INFO level]

If you are using a single map extract, I guess that the valid situation 
for the UK is that there are no incomplete coastlines in the map 
extract, except maybe for (North) Ireland. For most other countries with 
a coastline, you have to somehow tell splitter or mkgmap to augment the 
lsat bit of coastline, or to ensure that your tile borders clip the map 
before the end of the coastline. I do that for my map of Finland 
<http://www.polkupyoraily.net/osm/>. The SE end of the mainland 
coastline is clipped by my carefully chosen tile boundary, and the NW 
end is augmented to the tile boundary by mkgmap.

If you are using multiple map extracts that partly overlap, then I guess 
that you should be expecting trouble.

Best regards,

	Marko