For Census the SRID is 4269 and then you can reproject to 2163 (US National Atlas - which maintains measurement at least for continental US) or a particular UTM zone or state plane (both good for measurement but serve smaller areas) or mercator (which doesn't seem terribly good for measurement but has some other advantages such as shape and covering wider area).
To figure out the right SRID for what your native data we usually look at the prj file if any and then run a query like this SELECT * FROM spatial_ref_sys WHERE srtext ILIKE '%GCS%' AND srtext ILIKE '%1983%' AND proj4text ILIKE '%NAD83%' AND proj4text ILIKE '%longlat%' To convert to UTM zone SRID for your particular - take a look at this function in WIKI - utmzone - it will return the SRID of UTMZone of a geometry. Then you can use ST_Transform to convert from 4269 to whatever you decide. Hope that helps, Regina and Leo -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Lee Hachadoorian Sent: Tuesday, March 11, 2008 10:35 PM To: PostGIS Users Subject: [postgis-users] SRID and unprojected (Census) data Can someone please give me some ideas, or pointers to where this question is answered elsewhere, on how to handle unprojected geographic data in PostGIS? Would I just create the table with SRID = -1? The US Census makes several cartographic boundary files available using the NAD83 datum, but unprojected (with just lat/long coordinates for each point or polygon). I looked through spatial_ref_sys, and there are over 500 NAD83 reference systems, but it appears that they are all projected (UTM, state plane, whatever). Thanks in advance, Lee Hachadoorian PhD Student, Geography Program in Earth & Environmental Sciences CUNY Graduate Center _______________________________________________ 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
