The most important sources of morphological information have been the large catalogues of galaxies produced since the 1960's. Morphological classifications on the de Vaucouleurs revised Hubble system available prior to 1976 for some 4400 galaxies are summarized in RC2. A standard reference for morphology for many years, RC2 will soon be replaced by RC3 (de Vaucouleurs et al., 1991; see below).
Sandage and Tammann in the RSA have applied Hubble's own revision (with modifications) to the 1,246 galaxies in the old Shapley-Ames all-sky survey of bright galaxies, the southern part of which is based in part on a Las Campanas imaging survey described by Dressler and Sandage (1978) and Sandage and Brucato (1979). This is a valuable source for morphology for a relatively well-defined sample. High quality photographs of many of these objects are provided in Sandage and Bedke (1988). Dressler (1980b) also applied the Hubble-Sandage system to thousands of galaxies in 55 rich clusters. A recent application of the Yerkes system was made by Wirth and Gallagher (1980) in the Hydra I and Fornax Clusters based in part on CTIO 4-m prime focus plates. Because of the great recent interest in the so-called "Great Attractor", van den Bergh (1989) gives RDDO classifications for several hundred spirals in that direction.
The Palomar Sky Survey led to some of the largest catalogues of morphological information ever produced. These include the UGC (Nilson, 1973) and the MCG (see Vorontsov-Velyaminov, 1987 and references therein). The more recently produced ESO-B and SERC sky surveys have also proven to be gold-mines for morphology in the zones south of declination -17°. Hubble types based on the ESO-B survey are provided for 16,000 galaxies by Lauberts (1982), while Corwin, de Vaucouleurs, and de Vaucouleurs (1985) took advantage of the much finer grained and deeper SERC films and plates to produce the Southern Galaxy Catalogue (or SGC), which includes, among other things, detailed de Vaucouleurs revised Hubble types and DDO luminosity classes for 5,364 galaxies. This was followed by the Extension to the Southern Galaxy Catalogue (ESGC, Corwin and Skiff, 1990, in preparation), which provides more accurate type information (based on Palomar I copy plates) in the little studied zone from -17° < < -2°.
More specialized catalogues have also been based the SERC charts or their northern equivalent, the Palomar II Sky Survey. For example, the SERC survey has been used for the Atlas of Southern Peculiar Galaxies and Associations (Arp and Madore, 1987) and the Catalogue of Southern Ringed Galaxies (or CSRG, see Buta, 1986a, 1991a), while the PSS II is being used to compile new lists of northern low surface brightness galaxies (Schombert and Bothun, 1988).
Finally, RC3 continues the tradition of its predecessors RC1 and RC2 in bringing together basic information on many galaxies from a variety of sources, including morphological types. The types are based on 10 sources, but mainly the large databases in RC2, SGC, ESGC, UGC, and CSRG. The overlap among these different sources was used to make triangular comparisons between estimates of the coded numerical de Vaucouleurs stage index, T, which allowed estimates of the mean errors of each type and checks on the reproducibility of the system. In a detailed analysis by S. Mitra first, and later by myself, it was found that scale errors and zero point differences between sources are small and that, on average, the error of an estimate of T (not marked * or ?) for a galaxy having D25 = 2' and axis ratio R25-1 = 0.6 is (T) ~ 0.7. Since the vast majority of types from these sources are based on the small-scale sky surveys, this error is representative of those types and not types based on large scale plates taken with 2.5-5m class telescopes, which should be considerably better. The comparisons confirmed that the revised Hubble system is reproducible at a reasonable level of certainty. Combining all sources, RC3 gives types for 17,775 galaxies and is the largest source of Hubble morphological type information ever produced.