Dan, Thanks, that was a really good intro to get my head wrapped around some of the concepts, as this is all new to me.
Instead of reprojecting my data, I found that I could use the ST_Transform and ::geography cast to have ST_Area return the geography area instead, a la (snippet follows). This is fine, and performance isn't an issue as I'm working with this data statically. select ST_Area(ST_Transform(the_geom,4326)::geography) AS area from ... <snip> Hope this helps someone else.. Thanks again! On May 20, 2011, at 12:00 PM, [email protected] wrote: Hi Peter, Here is a link to OSGeo workshop that should be a helpful premier on the issue in general and provides a solution to your problem through the use of PostGIS's geography type: http://workshops.opengeo.org/postgis-intro/geography.html If you are dealing with a fairly well define area, say the West Coast of the US and Canada, then you might consider reprojecting your data out of NAD83 (North American Datum of 1983) geographic (lon/lat) coordinates (EPSG: 4269) into Euclidean coordinates (such as NAD83 UTM 10N), and then you can use the standard st_area tool and the result will be in meters. Dan On 05/20/2011 11:57 AM, Peter Hsu wrote: > I have a simple question. I've loaded up shape files from the tigerline US > census bureau. Everything works fine, but I'm trying to find the area of a > geometry in meters. However, I'm only able to get the area in SRID units. > > How can I convert from SRID units to meters? Is this a linear conversion? > Or is it dependent on the latitude of the area in question? > > The SRID for the tigerline files is 4269 > > Peter > _______________________________________________ > postgis-users mailing list > postgis-users at postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users
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