[postgis-users] trouble getting correct units from "area(transform"

[Charles Blankenship]

Disclaimer: I'm very new to GIS.

I want to calculate the areas of school districts in Nevada (and
California at some point) using census shape files.
http://www.census.gov/geo/cob/bdy/sn/sn00shp/sn32_d00_shp.zip

The data is unprojected so I know I must project it onto something good
for equal areas.  I'm trying NAD83 California Albers (SRID = 3310).

It seems to me from reading the documentation and numerous other
posts/tutorials, that the following code should return the area of the
districts in meters (or something I can convert to meters).

select area(transform(the_geom, 3310)) from mytable

This returns a column of areas which match my unprojected areas exactly!

I've fiddled with setting the constraint to SRID=3310, importing through
the qGIS SPIT plugin, selecting into a new table, delete and resetting
constraints, and on and on...


FWIW, I can load the file into qGIS, set the projection to 3310, and the
identify area feature calculates the "derived area" exactly as it should
be.  I can't for the life of me figure out how to even get into the
approximately correct units.  (I've tried reprojecting to quite
different SRIDs and can see the area change slightly, but it still
appears to be in native map units or degrees).

Thanks for any assistance,
Charles