5.3. Catalogues of Direct Plates
While the object catalogues mentioned above were drawn from homogeneous sky surveys, there are almost 2 million wide-field photographic plates archived at individual observatories around the world (see the Newsletters of the IAU Commission 9 ``Working Group on Sky Surveys''). To allow the location and retrieval of such plates for possible inspection by eye or with scanning machines, the ``Wide-Field Plate Database'' (WFPDB) (www.skyarchive.org) is being compiled and maintained at the Institute of Astronomy of the Bulgarian Academy of Sciences. As described by [Tsvetkov et al. (1998)], the WFPDB offers metadata for currently ~ 330,000 plates from 57 catalogues (see http://www.skyarchive.org) collected from more than 30 observatories. Since August 1997 the WFPDB may be searched as catalogue VI/90 via the CDS VizieR catalogue browser (vizier.u-strasb.fr/cats/VI.htx).