[postgis-users] [Postgis-User] Different between geometry and geography?

[nguyen liem]

Hi everyone,
http://postgis.refractions.net/docs/ST_DWithin.html
I see the ST_DWithin function that we can we can determine the geometries
are within a specified distance of one another.
*
ST_DWithin*(*geometry* g1, *geometry *g2, double precision distance_of_srid)
;
*ST_DWithin*(*geography* gg1, *geography *gg2, double precision
distance_meters);

Could you explain me when we use *geometry *and when *geography*.
    Geometry which is a geometry tupe: POINT, LINE, POLYGON ... ?
    Geography: ...?
    ...

Cheers.

-- 
Liem Nguyen
Developer
Axon Active Corp.
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