[postgis-users] Using PostGIS for partial intersection/union of many polygons

[Sparr]

On Wed, Jul 31, 2013 at 5:54 AM, Rémi Cura <remi.cura at gmail.com> wrote:
> Hey,
> my 2 cents (sorry I can't access your example)
>
> Depending on what you want, you may have interest in sampling :
> you create a grid of point (there is a function) or a grid of polygon
> square.
> Then you compute for each point(square) the number of polygon it is in (on
> simple sql query invovling count(*) OVER and st_intersects)
> Then when you want space where there are between N and M polygons
> overlaying, you just query the table with point/square with a WHERE count >N
> and count <M.
>
> It should run very fast, even fater if you put btree index on the count
> result.
> I don't know what you want, but if this is some kind of indicator, sampling
> may be legitimate.
> If you want crisp boundary, it may be used to fasten computing (doing the
> precise computing only on polygons on border)

I would prefer not to resort to sampling. Some of the boundaries are
drawn arbitrarily precisely, and I'd like to preserve that precision.

http://regionaldifferences.com/results.html?region=New%20England&lat=42&lon=-73&zoom=6
(now with 708 polygons)