The European Petroleum Survey Group (EPSG; now defunct, and superseded by the OGP Surveying and Positioning Committee) created and maintains a spatial reference database, assigning EPSG code numbers to spatial reference systems (combinations of coordinate systems, projections, and datums). There really is no way to figure out the spatial reference system from just the code number alone, or vice versa, so you need to look them up. The official database is in Microsoft Access format, not terribly easy to use; the code list in tabular format isn’t much better. There’s now a convenient online version of the database, searchable by keywords or code number. You can then access additional information for that spatial reference system in a number of different formats:
- Human-Readable OGC WKT
- OGC WKT
- ESRI WKT
- MapServer Mapfile
- PostGIS spatial_ref_sys INSERT statement
Users can also upload their own spatial reference definitions, which I suppose is a good thing as long as you exercise caution in using them.