[OSM-talk] Tagging hierarchies

[Robin Paulson]

On 14/01/2008, 80n <80n80n at gmail.com> wrote:
> > On 14/01/2008, Alex Mauer <hawke at hawkesnest.net> wrote:
> > > Robin Paulson wrote:
> > > > the point i'm trying to get across, is that all water features, be
> > > > they linear (rivers, canals, stream) or areas (lakes, reservoirs) or
> > > > whatever would benefit from being under _one_ top-level tag, for
> > > > consistency.
> > >
> > > Hmm, are you sure?  Is it easy for a renderer to differentiate a linear
> > > feature from an area without a distinct tag?  I don't think it could be.
> >
> > yes, of course - in exactly the same way as you can differentiate a
> > square, triangle or circle drawn on paper, from a line
> >
> > areas must form complete loops, otherwise they are treated as ways by
> > the renderer
> >
>
> This is not true.  Osmarender does not require areas to be closed in order
> to render them.  It automatically joins the last node to the first node if
> it has been asked to render an area.

ok, that's interesting, i didn't know that. why does it do that, and
can anyone comment if mapnik is the same?

getting back to the original point: this won't cause a problem - if
all items tagged waterway=lake are added to the renderer rules as
areas or nodes (and only areas or nodes), and all items tagged as
waterway=rivers are added as ways (and only ways) then the renderer
will be able to handle them appropriately.

from what i can see, wide rivers are tagged with riverbanks, similarly
to coastlines, so there's no ambiguity there either