Constraining the Galactic structure parameters with the XSTPS-GAC and
  SDSS photometric surveys
  Photometric data from the Xuyi Schmidt Telescope Photometric Survey of the
Galactic Anticentre (XSTPS-GAC) and the Sloan Digital Sky Survey (SDSS) are
used to derive the global structure parameters of the smooth components of the
Milky Way. The data, which cover nearly 11,000 deg$^2$ sky area and the full
range of Galactic latitude, allow us to construct a globally representative
Galactic model. The number density distribution of Galactic halo stars is
fitted with an oblate spheroid that decays by power law. The best-fit yields an
axis ratio and a power law index $\kappa=0.65$ and $p=2.79$, respectively. The
$r$-band differential star counts of three dwarf samples are then fitted with a
Galactic model. The best-fit model yielded by a Markov Chain Monte Carlo
analysis has thin and thick disk scale heights and lengths of $H_{1}=$ 322\,pc
and $L_{1}=$2343\,pc, $H_{2}=$794\,pc and $L_{2}=$3638\,pc, a local
thick-to-thin disk density ratio of $f_2=$11\,per\,cent, and a local density
ratio of the oblate halo to the thin disk of $f_h=$0.16\,per\,cent. The
measured star count distribution, which is in good agreement with the above
model for most of the sky area, shows a number of statistically significant
large scale overdensities, including some of the previously known
substructures, such as the Virgo overdensity and the so-called "north near
structure", and a new feature between 150\degr $< l < $ 240\degr~and $-1$5\degr
$< b < $ $-$5\degr, at an estimated distance between 1.0 and 1.5\,kpc. The
Galactic North-South asymmetry in the anticentre is even stronger than
previously thought.
