Hi be careful with units. This formula returns the area using projection's units (degrees, meters, kilometers etc). If that's the case maybe convert to some metric projetion
UPDATE table1 SET area_column = ST_AREA(ST_TRANSFORM(the_geom, srid-of-metric-projection)); -- this returns, normally, square meters. The problem is chose the right projection for your data (maybe more than one). Luigi Castro Cardeles 2009/4/3 George Silva <[email protected]> > Hello Aurora, > > In ArcGIS it's all different. In PostGIS you can use simple/complex SQL > queries to "calculate values" in a similar fashion of arcgis. > > The simplest of them all would be, in your case: > > ALTER TABLE table1 ADD COLUMN area_column double precision; > UPDATE table1 SET area_column = ST_AREA(the_geom); > > You can in that SQL query divide, multiply, and do whatever you want with > that result that will be written to the column area_column. > > I hope that helps > > George > > > On Fri, Apr 3, 2009 at 12:55 PM, Aurora Geomatics < > [email protected]> wrote: > >> Hello PostGIS users, >> >> I have just installed William Kyng's PostgeSQ/PostGIS packages for Mac OS >> X.5 >> >> I have been playing with pgAdmin and QGIS with importing shapefiles into >> PostGIS. Works dandy. >> >> Now I am wondering how to solve Attribute Calculations. >> >> Years of using ArcGIS and GRASS it is pretty straightforward on those >> apps, and am stumped with PostGIS Attribute calculations.. >> >> For example, using a polygon feature; >> >> Creating a new column, say AREA and filling with a calculation that is >> Hectares. >> >> Thanks! >> _______________________________________________ >> postgis-users mailing list >> [email protected] >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> > > > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > >
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