david at frankieandshadow.com
Sat Feb 10 14:14:49 GMT 2007
> -----Original Message-----
> From: talk-bounces at openstreetmap.org
> [mailto:talk-bounces at openstreetmap.org]On Behalf Of Nick Whitelegg
> Sent: 10 February 2007 13:07
> To: talk at openstreetmap.org
> Subject: Re: [OSM-talk] landuse=urban
> On Saturday 10 Feb 2007 12:54, Tom Chance wrote:
> > Ahoy,
> > On Saturday 10 February 2007 12:18:28 Nick Whitelegg wrote:
> > > What would be useful I feel is a generic tag for any urban
> area, so that
> > > urban and countryside areas can easily be distinguished. landuse=urban
> > > seems a good choice. This would make it easy, for example, to draw an
> > > urban area based on the Landsat or Yahoo imagery. Any
> comments on this?
> > Just curious, what do we lack with
> > landuse=residential/retail/industrial/etc? If people use those
> then surely
> > entire urban areas are clearly marked off? If there are urban areas that
> > don't fit into those categories then we could expand the list.
> > Regards,
> > Tom
> The problem is that you might not know what is what, also it's
> more effort (could involve creating 50 areas rather than just
> one). If you're
> using Landsat imagery or Yahoo imagery outside of the
> high-resolution areas,
> you can easily tell what's urban and what isn't, but little more
> than that.
> That's not to say remove the finer-grained classification, but
> marking out
> whole urban areas with landuse=urban would make mapping which aims to
> distinguish between urban and non-urban areas much easier to generate.
You could always underlay everything else in an urban area with such an area
on layer=-5 say, then more specific things would show up on top.
However, I think there may be a way to do this automatically. Mst urban
areas have large numbers of residential streets, and by determining a local
envelope enclosing residential streets I think it might be possible to
generate a suitable background. This almost happens anyway with abbutters
egnerated for them, its justtehre are gaps, especially around roads one
wants to classify as e.g. primary within the urban envelope. This wouldn't
be perfectly accurate, of course, but would give the idea of a conurbation,
or even just a small village.
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