  We estimated the Galactic model parameters from the SDSS data reduced for two
fields in the anti-centre direction of the Galaxy, $l= 180^{o}$, and symmetric
relative to the Galactic plane, $b=+45^{o}$ and $b=-45^{o}$. The large size of
each field, 60 deg$^{2}$, and the faint limiting apparent magnitude, g=22, give
us the chance to determine reliable parameters for three components, thin and
thick discs and halo, in the north and south hemispheres of the Galaxy, except
the scalelengths for two discs which are adopted from Juri\'c et al. (2005).
Metallicities were evaluated by a recent calibration for SDSS, and absolute
magnitudes of stars with $4<M(g)\leq8$ were derived as a function of (g-r)
colour and metallicity. Conspicuous differences could not be detected between
the corresponding Galactic model parameters for the thin disc of north and
south fields, and our results are consistent with the ones in the literature.
The same case is valid for the halo, especially the axis ratios for two fields
are exactly equal, $\kappa=0.45$. The metallicity distribution for unevolved G
type stars with $5<M(g)\leq6$ shows three substructures relative to the
distance from the Galactic plane: for $z^{*}<3$ kpc, the metallicity gradient
for two fields is $d[M/H]/dz \sim -0.20(\pm0.02)$ dex kpc$^{-1}$, consistent
with the formation scenario of the thin disc. For $5<z^{*}<10$ kpc, $d[M/H]/dz
\sim -0.03(\pm0.001)$ dex kpc$^{-1}$ for two fields, confirming that the
metallicity gradient for the halo component is close to zero. When we combine
these substructures, however, we find a smooth metallicity gradient for two
fields, $-0.30(\pm0.04)$ dex kpc$^{-1}$.
