[Tagging] natural=bay as nodes are evil

Christoph Hormann chris_hormann at gmx.de
Mon Oct 27 10:44:45 UTC 2014


On Monday 27 October 2014, moltonel 3x Combo wrote:
> >
> > If you think about it a bit and do not try to place the node where
> > you would place the label (which depends on the map projection
> > anyway) properly placing a node for a bay is usually quite simple. 
> > The most difficult are long, fjord-like bays where a way along them
> > would be more appropriate.
>
> I'm really curious what your method to figure out the bay area from
> the node is, because even as a human I find that most bay nodes can
> lead to many different interpretations.

There are a lot of different possibilities to approach this.  A very 
simple method would be:

- find the point on the coastline closest to the bay node.
- collect all coastline segments within 2-3 times the distance of the 
closest node.
- connect all open ends of these coastlines with the closest other open 
end.
- assemble a polygon and use it.

This extremely simple approach will probably result in reasonable 
polygons for label placement in more than half the cases.  You can 
easily improve the algorithm of course to properly deal with various 
special cases, in particular the case of small islands within a bay 
deserves consideration.

> Some coastline ways would belong to more relations, so what ? They
> already usually belong to 3-4 administrative boundary relations,

Yes - and boundary relations are well known to be constantly broken and 
a pain to maintain even for experienced mappers.

-- 
Christoph Hormann
http://www.imagico.de/



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