The GSC contains roughly objects with magnitudes in the range 7 - 16, of which more than are classified as stars. It is based on an all-sky, single epoch, single passband Schmidt survey. Astrometry, at equinox J2000, is available at the epoch of the individual plates used in the GSC (1975 - 1983) and is based on the AGK3, SAO and CPC catalogues. An analysis against CAMC measurements by Taff et al. (1990) showed that the GSC absolute positional errors are dominated by systematic effects and vary from 0.5 - 1.1 arcsec from plate centre to edge in the north and from 1.0 - 1.6 arcsec in the south. Relative errors at separations vary from 0.3 - 0.8 arcsec, depending on hemisphere and magnitude. The positions are therefore not quite accurate enough to be used for blind offsetting into narrow slits.
The catalogue is subdivided into 9537 regions bounded by small circles of right ascension and great circles of declination. Data for each region are stored in separate files; these files are contained in subdirectories, each of which covers a range of declination. The GSC is distributed on two CD ROMs in ISO 9660 format, divided at a declination of S. All data files are in FITS table format. The catalogue is fully documented in the booklet supplied with the CD-ROM set and a series of papers (Lasker et al. 1990, Russell et al. 1990 and Jenkner et al. 1990).