[OSM-talk] Ditches

Richard Mann richard.mann.westoxford at googlemail.com
Tue Dec 15 12:56:19 GMT 2009

I guess we have to decide whether culverts or fords are the more common (and
explicitly tag the less-common). I'd plump for culverts being significantly
more common myself, but that might not be true on a whole-world basis.


On Tue, Dec 15, 2009 at 12:49 PM, Peter Childs <pchilds at bcs.org> wrote:

> 2009/12/15 John Smith <deltafoxtrot256 at gmail.com>:
> > 2009/12/15 Steve Bennett <stevagewp at gmail.com>:
> >> IMHO, tagging "layer=1 bridge=yes" for a road going over water is an
> >> example of a hack, and "tagging for the renderer". The information
> >> "bridge=1" is more than enough to render with, so "layer=1" can *only*
> >> be interpreted as giving a renderer a crutch.
> >
> > Without layer information you'd be guessing if the road goes over the
> > water or the water goes over the road, or the water and road are at
> > the same level.
> >
> > You could come up with sane defaults, but that's making assumptions
> > rather than tagging explicitly so you know beyond a reasonable doubt.
> >
> If you have a bridge or a tunnel you don't need a layer tag a bridge
> infers it "goes over" a tunnel that it "goes over"
> If there is neither a tunnel, or a bridge and no layer either then it
> must be a ford.
> If you mark bridge=yes, layer=1 you are repeating your self. which is
> where problems start, see database normalisation.
> Peter.
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