The Last of FIRST: The Final Catalog and Source Identifications
  The FIRST survey, begun over twenty years ago, provides the definitive
high-resolution map of the radio sky. This VLA survey reaches a 20cm detection
sensitivity of 1 mJy over 10,575 deg**2 largely coincident with the SDSS area.
Images and a catalog containing 946,432 sources are available through the FIRST
web site (http://sundog.stsci.edu). We record here the authoritative survey
history, including hardware and software changes that affect the catalog's
reliability and completeness. We use recent JVLA observations to test the
survey astrometry and flux bias/scale. Our sidelobe-flagging algorithm finds
that fewer than 10% of the catalogued objects are likely sidelobes; these are
faint sources concentrated near bright sources, as expected. A match with the
NRAO VLA Sky Survey shows very good consistency in flux scale and astrometry.
Matches with 2MASS and SDSS indicate a systematic 10-20mas astrometric error
with respect to the optical reference frame in old VLA data that has
disappeared with the advent of the JVLA. We demonstrate strikingly different
behavior between the radio matches to stellar objects and to galaxies in the
optical and IR surveys reflecting the different radio populations present over
the flux density range 1-1000 mJy. As the radio flux density declines, quasars
get redder and fainter, while galaxies get brighter and have colors that
initially redden but then turn bluer near the FIRST detection limit.
  Implications for future radio sky surveys are also discussed. In particular,
we show that for radio source identification at faint optical magnitudes, high
angular resolution observations are essential, and cannot be sacrificed in
exchange for high signal-to-noise data. The value of a JVLA survey as a
complement to SKA precursor surveys is briefly discussed.
