[OSM-talk] best way to map large areas

[Andy Allan]

On Nov 29, 2007 11:25 PM, Robin Paulson <robin.paulson at gmail.com> wrote:
> On 30/11/2007, Andy Allan <gravitystorm at gmail.com> wrote:
> > > that was the way i originally considered, but then i found that
> > > smaller areas will render on top of a larger one. i was going to
> > > create a large residential area covering a big part of the city, and
> > > then drop retail and industrial areas, aprks, schools, etc. (all
> > > smaller than the residential area) on top of that. a lot less fiddly
> > > to make
> >
> > You can't really do it that way*. A given point should only lie within
> > the boundaries of whichever landuse areas are appropriate - so if it's
> > purely industrial, it shouldn't lie within a (larger) residential
> > area. Generally the main ones that make sense are overlapping
> > commercial and residential, to show that there are shops and housing
> > at the same coordinates.
>
> ok, that sounds reasonable - i had assumed the renderer would subtract
> one are from the other, to leave an area with a hole in it, and a
> smaller area filling that hole (does it do that?)

There's multiple renderers, so I can't generalise. But no, I don't
think any renderer does this, beyond just painting one over the top of
the other. If you consider non-visual uses of the data, such as
calculating how many square metres a given area covers, that's another
reason to be careful with overlapping.

> taking your point to it's extreme: how can there be shops and houses
> at the same point? i generally try to make my landuse areas as precise
> and accurate as possible, so small areas of shops get a small area,
> which exactly matches the extremity of the block of shops. if there
> are a few houses amongst a block of shops, they gets their own area,
> no matter how small

As Rob said, shops with houses above
(http://flickr.com/photos/themeldrums/53334911/) is the canonical
example for legitimate overlapping landuse areas, but I'm sure there's
other possibilities too.

Cheers,
Andy