  We performed a photometric multicolor survey of the core of the Canis Major
over-density at l 244, -8.0, reaching V = 22 and covering 0.3 x 1 degree. The
main aim is to unravel the complex mixture of stellar populations toward this
Galactic direction, where in the recent past important signatures of an
accretion event have been claimed to be detected. While our previous
investigations were based on disjointed pointings aimed at revealing the large
scale structure of the third Galactic Quadrant, we now focus on a complete
coverage of a smaller field centered on the Canis Major over-density. A large
wave-length baseline, in the UBVRI bands, allows us to build up a suite of
colour colour and colour magnitude diagrams, providing a much better diagnostic
tool to disentangle the stellar populations of the region. In fact, the simple
use of one colour magnitude diagram, widely employed in all the previous
studies defending the existence of the Canis Major galaxy, does not allow one
to separate the effects of the different parameters (reddening, age,
metallicity, and distance) involved in the interpretation of data, forcing to
rely on heavy modeling. In agreement with our previous studies in the same
general region of the Milky Way, we recognize a young stellar population
compatible with the expected structure and extension of the Local (Orion) and
Outer (Norma-Cygnus) spiral arms in the Third Galactic Quadrant. Moreover we
interpret the conspicuous intermediate-age metal poor population as belonging
to the Galactic thick disk, distorted by the effect of strong disk warping at
this latitude, and to the Galactic halo.
