[OSM-talk] Coastline updates

[Jochen Topf]

On Mon, Nov 18, 2013 at 06:08:40PM +0100, Christoph Hormann wrote:
> On Monday 18 November 2013, Jochen Topf wrote:
> > Hi!
> >
> > For the last about two weeks we haven't gotten any coastline updates
> > through. The problem is that every day there is something broken
> > somewhere with the coastline. Often problems get fixed the same day,
> > but new problems show up the next.
> >
> > I have now changed the coastline update process from "once a day" to
> > "once every 4 hours". This means updates show up quicker in the OSM
> > Inspector at http://tools.geofabrik.de/osmi/?view=coastline .
> 
> Sounds good.  This should also increase the chance that if you see an 
> error in the OSMI it is not already fixed (which is very common at the 
> moment and somewhat annoying of course).
> 
> How sensitive is your system by the way in discarding a coastline as 
> broken?  Obviously any unfixable error in one of the four large 
> continental coastlines will trigger it.  Same for large islands like 
> Greenland and New Guinea i suppose.  But there probably is a limit.  
> There have for example been many coastline errors in the Philippines 
> recently due to recent mapping activity there but many on fairly small 
> islands.

Well, one reason for the missing updates in the last weeks was that I
increased the sensitivity after the whole of Ireland went missing and
my process didn't notice it.

The many small islands aren't the problem. The typical problem is somebody
messing up the coastline of something larger, maybe even one of the continents.
Typically there is a small or large gap in the coastline. If the gap is
small enough, osmcoastline tries to close it, but that often leads to
to self-intersections of the coastline.

The other typical case is somebody adding a new coastline to a pre-existing
one. In most cases to add more detail from sat images. In this case they
should move the old coastline, but people often don't. This way you have
open ends somewhere and even if the software tries closing them you'll get
overlaps etc.

Jochen
-- 
Jochen Topf  jochen at remote.org  http://www.jochentopf.com/  +49-721-388298