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PostGIS 1.5.8 Manual22 / 3104.3.1 The SPATIAL_REF_SYS Table and Spatial Reference SystemsThe spatial_ref_sys table is a PostGIS included and OGC compliant database table that lists over 3000 known spatial referencesystems and details needed to transform/reproject between them.Although the PostGIS spatial_ref_sys table contains over 3000 of the more commonly used spatial reference system definitionsthat can be handled by the proj library, it does not contain all known to man and you can even define your own custom projectionif you are familiar with proj4 constructs. Keep in mind that most spatial reference systems are regional and have no meaningwhen used outside of the bounds they were intended for.An excellent resource for finding spatial reference systems not defined in the core set is http://spatialreference.org/Some of the more commonly used spatial reference systems are: 4326 - WGS 84 Long Lat, 4269 - NAD 83 Long Lat, 3395 -WGS 84 World Mercator, 2163 - US National Atlas Equal Area, Spatial reference systems for each NAD 83, WGS 84 UTMzone - UTM zones are one of the most ideal for measurement, but only cover 6-degree regions.Various US state plane spatial reference systems (meter or feet based) - usually one or 2 exists per US state. Most of the meterones are in the core set, but many of the feet based ones or ESRI created ones you will need to pull from spatialreference.org.For details on determining which UTM zone to use for your area of interest, check out the utmzone PostGIS plpgsql helperfunction.The SPATIAL_REF_SYS table definition is as follows:CREATE TABLE spatial_ref_sys (srid INTEGER NOT NULL PRIMARY KEY,auth_name VARCHAR(256),auth_srid INTEGER,srtext VARCHAR(2048),proj4text VARCHAR(2048))The SPATIAL_REF_SYS columns are as follows:SRID An integer value that uniquely identifies the Spatial Referencing System (SRS) within the database.AUTH_NAME The name of the standard or standards body that is being cited for this reference system. For example, "EPSG"would be a valid AUTH_NAME.AUTH_SRID The ID of the Spatial Reference System as defined by the Authority cited in the AUTH_NAME. In the case ofEPSG, this is where the EPSG projection code would go.SRTEXT The Well-Known Text representation of the Spatial Reference System. An example of a WKT SRS representation is:PROJCS["NAD83 / UTM Zone 10N",GEOGCS["NAD83",DATUM["North_American_Datum_1983",SPHEROID["GRS 1980",6378137,298.257222101]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-123],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1]]For a listing of EPSG projection codes and their corresponding WKT representations, see http://www.opengeospatial.org/.For a discussion of WKT in general, see the OpenGIS "Coordinate Transformation Services Implementation Specification"at http://www.opengeospatial.org/standards. For information on the European Petroleum Survey Group (EPSG) and theirdatabase of spatial reference systems, see http://www.epsg.org.