[postgis-users] Union and Intersection of Polygon layers

[Kevin Neufeld]

The PostGIS wiki has some thoughts on overlays ...

http://trac.osgeo.org/postgis/wiki/UsersWikiExamplesOverlayTables

Paul Ramsey wrote:
> Union is trivial. Here's a query that generates a new set of polygons
> dissolved based on an attribute value:
>
> create table newtable as select st_union(the_geom), attribute group by
> attribute;
>
> Overlay is non-trivial, and I leave that to someone else to provide
> good SQL. The simple case of finding all the overlapping parts is
> easy, but filling in the non-overlapping parts is harder.
>
> P
>
> On Mon, Sep 21, 2009 at 3:32 PM, Ravi <ravivundavalli at yahoo.com> wrote:
>   
>> Hi,
>> am using other FOSS GIS GRASS and OpenJUMP for
>> Polygon layers Union
>>           and Intersection (overlay)
>> are there similar functions in postGIS THE LATEST RELEASE
>>
>> I have raised these issues some time before too.
>> http://postgis.refractions.net/pipermail/postgis-users/2008-May/019515.html
>>
>> Ravi Kumar
>>
>>
>>
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>>     
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