  We present a new theoretical population synthesis model (the Galaxy Model) to
examine and deal with large amounts of data from surveys of the Milky Way and
to decipher the present and past structure and history of our own Galaxy. We
assume the Galaxy to consist of a superposition of many composite stellar
populations belonging to the thin and thick disks, the stellar halo and the
bulge, and to be surrounded by a single dark matter halo component. A global
model for the Milky Way's gravitational potential is built up self-consistently
with the density profiles from the Poisson equation. In turn, these density
profiles are used to generate synthetic probability distribution functions
(PDFs) for the distribution of stars in colour-magnitude diagrams (CMDs).
Finally, the gravitational potential is used to constrain the stellar
kinematics by means of the moment method on a (perturbed)-distribution
function. Spiral arms perturb the axisymmetric disk distribution functions in
the linear response framework of density-wave theory where we present an
analytical formula of the so-called `reduction factor' using Hypergeometric
functions. Finally, we consider an analytical non-axisymmetric model of
extinction and an algorithm based on the concept of probability distribution
function to handle colour magnitude diagrams with a large number of stars. A
genetic algorithm is presented to investigate both the photometric and
kinematic parameter space. This galaxy model represents the natural framework
to reconstruct the structure of the Milky Way from the heterogeneous data set
of surveys such as Gaia-ESO, SEGUE, APOGEE2, RAVE and the Gaia mission.
