Philosophical point: Creating a column and filling it with a property of GEOMETRY like ST_Area() or ST_Length() is something which makes sense in a legacy GIS like Arc* or GRASS, where attributes are handled separately from spatial. In a spatial database, where the GEOMETRY is co-equal to the other columns, there is not much point, unless you are doing it for export purposes (filling in a column before exporting to shapefile for consumption by a legacy GIS).
What does having AREA in a column gain you? Now you can do math and tests against it? Well, in database land, you can do that already, just do you math and tests against the ST_Area() function directly. Paul 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 > > _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
