[OSM-dev] Very long ways have been split (was: Status of Database Server after 0.4 Upgrade: Fragile)

Jon Burgess jburgess777 at googlemail.com
Mon May 14 23:37:30 BST 2007


On Mon, 2007-05-14 at 23:13 +0100, Jon Burgess wrote:
> On Mon, 2007-05-14 at 01:08 +0200, Frederik Ramm wrote:
> > Hi,
> > 
> > >> The coastline display in tiles at home is solved; I don't know how Mapnik 
> > >> deals with it but Mapnik cannot reasonably expect us to have one way for 
> > >> the whole coastline of a continent. 
> > > 
> > > Mapnik does not expect t at h to do anything. It only worries about how it
> > > renders data.
> > 
> > So how does Mapnik render coastlines (and the water that is on one side 
> > of the coastline) currently, given that the coastline of anything but 
> > the tiniest islands is not closed?
> > 
> 
> For zoom 0..9 mapnik uses the VMAP0 shapefiles to define the countries
> and sea. At zoom 10+ the VMAP0 data is too inaccurate to be used so
> it renders the coast line as just a thin blue line with no concept of
> which side is land/sea.
> 
> For a small area of the globe (principally around the UK I believe)
> Artem has manually imported the OSM coastline data into a shapefile
> which is used at higher zooms. This needed some time and effort since
> the data in the shapefile had to be fixed up so that the coastline was a
> single continuous polygon.
> 
> See
> http://www.openstreetmap.org/index.html?lat=52.5740&lon=-1.8576&zoom=13
> 
> for an example of where the blue coast is used instead of vmap0 if you
> zoom out.
> 
> 
> > I was under the impression that this was somehow working. If it is: 
> > Could the same mechanism not be used for other things (such as lakes) as 
> > well? And if it isn't: Then why make a fuss about 19 lakes?
> 
> Yes, provided people step up to help Artem generate the appropriate
> shapefiles from raw OSM data. He requested people to help do this some
> months ago, see
> http://lists.openstreetmap.org/pipermail/talk/2007-March/012418.html 
> 

I think this earlier thread gives a few more details about the process
used
http://lists.openstreetmap.org/pipermail/talk/2007-February/010879.html

It seems no one else bought into the idea of moving the coastline data
out of the OSM DB.

	Jon






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