[postgis-users] Calculating Attributes

[George Silva]

PgAdmin can do it. The terminal can do it too, but i find pgAdmin more easy
to work with.

Just go to the database you are working, open a query editor and try it.

Dont forget about the considerations all the other made. The value returned
will depend on your projection.

george

On Fri, Apr 3, 2009 at 1:48 PM, Aurora Geomatics
<aurorageomatics at gmail.com>wrote:

> Thank you George,
> On 3-Apr-09, at 9:22 AM, George Silva wrote:
>
> 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.
>
>
> Pretty straight forward SQL statement.
> Is this a matter of opening a Terminal session using psql monitor?
>
> Is it possible through pgAdmin or QGIS?
>
> Thanks.
>
> I hope that helps
>
> George
>
> On Fri, Apr 3, 2009 at 12:55 PM, Aurora Geomatics <
> aurorageomatics at gmail.com> 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!
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>>
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