[OSM-talk] Best way to draw areas with holes?

[Chris Hill]

> Alex Mauer wrote:
> > Chris Hill wrote:
> > 
> > I have used the multipolygon relation to draw islands in rivers. 
> >It
> 
 >is specifically intended for drawing holes in areas and worked
> very
> 
 >well for me.
> > 
> 
> I've tried to use it for this, but I run into problems when the river
> bank is too large for a single way.  (I split the ways at 129
> nodes,
> 
 but
>  the exact number doesn't matter)
> 
> Here is the result:
> 
> http://www.informationfreeway.org/?lat=46.381337247472786&lon=-90.25169857324616
> &zoom=8&layers=B000F000
> 
> It appears to me that it mostly works, but then the renderer randomly
> decides to treat one of the islands with an "inner" role as if it had a
> role of "outer" instead of following the ring of "outer" ways.
> 
> 
I too broke a river into chunks, though it's smaller than your river. 
Each chunk has an area drawn with a clockwise way marked as waterway=riverbank.  The chunks butt up
to one another.  The islands have a way drawn anticlockwise, which is
important for the Osmarender renderer.  They are also tagged with waterway=riverbank.

You can take a look at:

http://www.openstreetmap.org/?lat=53.7207&lon=-0.7214&zoom=12&layers=0BF 



I modified Jon Burgess's step by step list from his email and added it to the relation Wiki page: 



http://wiki.openstreetmap.org/index.php/Relations/Multipolygon



This renders well at zoom 12 and higher, but lower zooms do not seem to render. 
 
cheers,Chris


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