We estimated the galactic model parameters for a set of 20 intermediate-latitude fields with galactic longitudes 0 ^ { \circ } \leq l \leq 100 ^ { \circ } and 160 ^ { \circ } \leq l \leq 240 ^ { \circ } , included in the currently available Data Release 6 ( DR6 ) of the Sloan Digital Sky Survey ( SDSS ) , to explore their possible variation with galactic longitude .
The local space densities of the thick disc and halo are almost the same for all fields , \langle ( n _ { 2 } / n _ { 1 } ) \rangle = 6.52 \% and \langle ( n _ { 3 } / n _ { 1 } ) \rangle = 0.35 \% , respectively , a result different than the one cited for high-latitude fields .
The thin disc ’ s scaleheight is 325 pc in the galactic centre changes to 369 pc in the third quadrant , which confirms the existence of disc flare , whereas the thick disc scaleheight is as large as 952 pc at galactic longitude l = 20 ^ { \circ } and 10 \% lower at l = 160 ^ { \circ } , which confirms the existence of the disc long bar in the direction l \simeq 27 ^ { \circ } .
Finally , the variation of the axis ratio of the halo with galactic longitude is almost flat , \langle ( c / a ) \rangle = 0.56 , except a slight minimum and a small maximum in the second and third quadrants , respectively , indicating an effect of the long bar which seems plausible for a shallow halo .
We estimated the metallicities of unevolved G–type stars and discussed the metallicity gradient for different vertical distances .
The metallicity gradient is d [ M / H ] / dz \sim - 0.30 dex kpc ^ { -1 } for short distances , confirming the formation of this region of the Galaxy by dissipational collapse .
However , its change is steeper in the transition regions of different galactic components .
The metallicity gradient is almost zero for inner halo ( 5 < z < 10 kpc ) , indicating a formation of merger or accretion of numerous fragments such as dwarf galaxies .

98.35.Ln Stellar content and populations ; morphology and overall structure , 98.35.Gi Galactic halo