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 the equator. 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).