  We used the ugr magnitudes of 1,437,467 F-G type main-sequence stars with
metal abundance -2<[Fe/H]<+0.2 dex and estimated radial and vertical
metallicity gradients for high Galactic-latitude fields (b>50) of the Milky Way
Galaxy. The radial metallicity gradient d[Fe/H]/dR=-0.042(0.011) dex/kpc
estimated for the stars with 1.31<z<=1.74 kpc is attributed to the thin-disc
population. While, the radial gradients evaluated for stars at higher vertical
distances are close to zero indicating that the thick disc and halo have not
undergone a radial collapse phase at least at high Galactic latitudes. The
vertical metallicity gradients estimated for stars with three different
Galactic latitudes, 50<b <=65, 65<b<=80 and 80<b<=90 do not show a strong
indication for Galactic latitude dependence of our gradients. The thin disc,
0.5<z<=2 kpc, with a vertical metallicity gradient d[Fe/H]/dz= -0.308(0.018)
dex/kpc, is dominant only in galactocentric distance (R) interval 6<R<=10 kpc,
while the thick disc (2<z<=5 kpc) could be observed in the intervals 6<R<=10
and 10<R<=15 kpc with compatible vertical metallicity gradients, i.e.
d[Fe/H]/dz= -0.164(0.014) dex/kpc and d[Fe/H]/dz= -0.172(0.016) dex/kpc. Five
vertical metallicity gradients are estimated for the halo (z>5 kpc) in three R
distance intervals, 6<R<=10, 10<R<=15 and 15<R<=20 kpc. The first one
corresponding to the interval 6<R<=10 kpc is equal to d[Fe/H]/dz= -0.023(0.006)
dex/kpc, while the others at larger R distances are close to zero. We derived
synthetic vertical metallicity gradients for 2,230,167 stars and compared them
with the observed ones. There is a good agreement between the two sets of
vertical metallicity gradients for the thin disc, while they are different for
the thick disc. For the halo, the conspicuous difference corresponds to the R
distance interval 6<R<=10 kpc, while they are compatible at higher R distance
intervals.
