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[mkgmap-dev] Sea 'bleeding' into land in northern France

From Thorsten Kukuk kukuk at suse.com on Fri Aug 5 15:45:57 BST 2022


On Fri, Aug 05, john510185 wrote:

> Hi, I hope someone can help with this. I'm a big fan of OpenMapChest and am
> amazed by Ben Konrath's lovely maps. There's a slight problem (of the first
> world type) in that in his map of Western Europe (specifically the Calais tile)
> the sea appears to have breached the sea wall and the land is inundated with
> blue! Ben says he can't help because it's due to a bad change someone has made
> to OSM. There's also something funny further west, around Le Havre. He says the
> problem will be solved by whoever made the change, but it's persisted now for
> quite a few iterations of his map.

Yes, the coastlines are very often broken in the OSM database, but for
the last days I couldn't find any serious problem in that area. There
are the usual wrong directions of islands, currently in the near of spain.
Depending on how he builds his maps and handles the coastline, this
could be a really big problem or no problem at all.

So it heavily depends on how he builds his maps.

> There does appear to be a conflict between his British Isles map and the one
> for Europe. However, the problem isn't replicated in OsmAnd, or in any of the
> other Garmin-related maps I use, which would suggest that OSM itself is OK.

Your assumption is wrong. The coastline is most of the time broken in
OSM, that's why people building maps have checks or use verified
coastline data to avoid this flooding. E.g. by using pre-build sea data
from here for garmin maps: https://www.thkukuk.de/osm/data/


> Any wisdom greatly appreciated!
> One of the replies I received was as follows:
> Those maps are generated with mkgmap, and this sort of problem happens
> occasionally when coastlines get broken in OSM. You might look at the
> archives for mkgmap-dev at lists.mkgmap.org.uk or perhaps post there
> directly.
> Any help with this would be much appreciated. I have MapSource screenshots
> available, but didn't attach them in case I messed anything up!
> Cheers!

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Thorsten Kukuk, Distinguished Engineer, Senior Architect
SUSE Software Solutions Germany GmbH, Frankenstraße 146, 90461 Nuernberg, Germany
Managing Director: Ivo Totev, Andrew Myers, Andrew McDonald, Martje Boudien Moerman
(HRB 36809, AG Nürnberg)

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