  We estimated the Galactic model parameters for a set of 36 high-latitude
fields included in the currently available Data Release 5 (DR 5) of the Sloan
Digital Sky Survey ({\em SDSS}), to explore their possible variation with the
Galactic longitude. The thick disc scaleheight moves from $\sim$550 pc at
$120^{\circ}<l<150^{\circ}$ to $\sim$720 pc at $250^{\circ}<l<290^{\circ}$,
while the thin disc scaleheight is as large as $\sim$195 pc in the anticenter
direction and $\sim$15% lower at $|l|<30^\circ$. Finally, the axis ratio
($c/a$) of the halo changes from a mean value of $\sim$0.55 in the two first
quadrants of the Galaxy to $\sim$0.70 at $190^{\circ}<l<300^{\circ}$. For the
halo, the reason for the dependence of the model parameters on the Galactic
longitude arises from the well known asymmetric structure of this component.
However, the variation of the model parameters of the thin and thick discs with
Galactic longitude originates from the gravitational effect of the Galactic
long bar. Moreover, the excess of stars in quadrant I (quadrant III) over
quadrant IV (quadrant II) is in agreement with this scenario.
