  We positionally match the 6 cm GB6, 20 cm FIRST and NVSS, and 92 cm WENSS
radio catalogs and find 16,500 matches in ~3,000 deg2 of sky. Using this
unified radio database, we construct radio "color-magnitude-morphology"
diagrams and find that they display a clear structure, rather than a random
scatter. We propose a simple, yet powerful, method for morphological
classification of radio sources based on FIRST and NVSS measurements. For a
subset of matched sources, we find optical identifications using the SDSS Data
Release 1 catalogs, and separate them into quasars and galaxies. Compact radio
sources with flat radio spectra are dominated by quasars, while compact sources
with steep spectra, and resolved radio sources, contain substantial numbers of
both quasars and galaxies.
