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 (SDSS), to explore their possible variation with the Galactic longitude. The thick disc scaleheight moves from similar to 550 pc at 120< l < 150 degrees to similar to 720 pc at 250 < l < 290 degrees, while the thin disc scaleheight is as large as similar to 195 pc in the anticenter direction and similar to 15% lower at vertical bar l vertical bar < 30 degrees. Finally, the axis ratio (c/a) of the halo changes from a mean value of similar to 0.55 in the two first quadrants of the Galaxy to similar to 0.70 at 190 < l < 300 degrees. 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.