[mkgmap-dev] State of the coastline art

Wed Mar 31 19:44:54 BST 2010

On Wed, Mar 31, 2010 at 09:27:19AM -0700, Apollinaris Schoell wrote:
> > Also, when debugging coastline errors (gap in coastline, coastline not
> > extending to map border), you may want to use a command like this:
> >
> > osmosis --rx finland.osm.bz2 --tf accept-ways natural=coastline --used-node
> > \
> > --wx finland-coastline.osm
> >
> >
> xapi is your friend and can achieve the same without downloading the planet
> or excerpts
> wget
> http://www.informationfreeway.org/api/0.6/way\[natural=coastline\]\[bbox=-124.5,32,-114,42\]-O
> coastline.osm

Yes, xapi can be useful if you are interested in particular features, but it
won't help you in debugging a problem with a particular planet extract.
The data may have changed since the extract was taken, or the extract may
not completely contain some features.  I prefer to work with extracts, because
I don't have access to a fast mirror of the OSM database that would quickly
produce country-size map extracts on demand.

Someone pointed out to me that the Geofabrik cutting polygons aren't set in
stone.  Indeed, I emailed Frederik Ramm today, and he promptly sent me the
boundary polygon in JOSM format.  I edited it slightly in order to exclude
or include a few islands, and sent it back.  It will be interesting to see
if tomorrow's extract works "out of the box" (with the exception of tweaking
the endpoints of the mainland coastline).  If not, in a few iterations it
will.  (Now that I think of it, I should also fix the broken lake
multipolygons near the Finnish-Russian border by editing the Geofabrik
cutting polygon.)

	Marko