[Tilesathome] Handling of multipolygons large than Z12 tile

[Ian Dees]

On Thu, May 21, 2009 at 9:59 PM, Rob Reid <rob at robreid.co.nz> wrote:

> Adam Schreiber wrote the following on 22/05/2009 06:22:
> > Has there been any work in osmarender/tiles at home on handling
> > multipolygons larger than a Z12 tile?  There's been an effort to
> > import US NHD data for water ways and bodies of water and often rivers
> > or lakes will cross tile boundaries causing problems like [1] [2].
> >
> > Cheers,
> >
> > Adam
> >
> > [1]
> http://informationfreeway.org/?lat=34.782449752666295&lon=-82.76998792819016&zoom=13&layers=B0000F000F
> > [2]
> http://informationfreeway.org/?lat=34.596345710140696&lon=-82.8900650353609&zoom=12&layers=B0000F000F
> >
> >
> So far I've only looked at the first example above, but as far as I can
> tell the problem is that osmarender does not currently support
> multipolygons with multiple outer ways.
> In the first example above the river has 5 waterway=riverbank ways with
> a role of outer. Osmarender just sees these as 5 unclosed ways which is
> why the results are a bit haphazard.


It might be helpful to only tag the relation with the waterway tags. That is
my interpretation of the proposal for extended multipolygons and (I think)
it is working so far for Mapnik. That's how I've been doing it up in
Wisconsin for a few subbasins-worth of NHD data.

(http://openstreetmap.org/?lat=46.3943&lon=-89.1034&zoom=14&layers=B000FTF)
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