  We estimated the scale-length of the thin disc with the J and W1 magnitudes
of the most probable Red Clump (RC) stars in the Galactic plane,
$-0\overset{^\circ}.5 \leq b \leq +0\overset{^\circ}.5$, in 19 equal sized
fields with consecutive Galactic longitudes which cover the interval $90^\circ
\leq l \leq 270^\circ$. Our results are constrained with respect to the solar
space density ($D^*=5.95$), which indicates that the radial variation of the
density is lower for higher Galactocentric distances. The scale-length of the
thin disc is 2 kpc for the fields in the Galactic anticentre direction or close
to this direction, while it decreases continuously in the second and third
quadrants reaching to a lower limit of $h$ = 1.6 kpc at the Galactic longitudes
$l$ = 90$^\circ$ and $l$ = 270$^\circ$. The distribution of the scale-length in
19 fields is consistent with the predictions from the Galaxia model and its
variation with longitude is probably due to the inhomogeneity structure of the
disc caused by the accreted material or other features such as warp and flare.
