The GLIMPSE ( Galactic Legacy Mid-Plane Survey Extraordinaire ) Point Source Catalog of \sim 30 million mid-infrared sources towards the inner Galaxy , 10 ^ { \circ } \leq|l| \leq 65 ^ { \circ } and |b| \leq 1 ^ { \circ } , was used to determine the distribution of stars in Galactic longitude , l , latitude , b , and apparent magnitude , m .
The counts versus longitude can be approximated by the modified Bessel function N = N _ { 0 } ( l / l _ { 0 } ) K _ { 1 } ( l / l _ { 0 } ) , where l _ { 0 } is insensitive to limiting magnitude , band choice , and side of Galactic center : l _ { 0 } = 17 ^ { \circ } -30 ^ { \circ } with a best fit value in the the 4.5 \mu m band of l _ { 0 } = 24 ^ { \circ } \pm 4 ^ { \circ } .
Modeling the source distribution as an exponential disk yields a radial scale length of H _ { * } = 3.9 \pm 0.6 kpc .

There is a pronounced north-south asymmetry in source counts for |l| ^ { < } _ { \sim } 30 ^ { \circ } , with \sim 25 % more stars in the north .
For l = 10 - 30 ^ { \circ } , there is a strong enhancement of stars of m = 11.5 - 13.5 mag .
A linear bar passing through the Galactic center with half-length R _ { bar } = 4.4 \pm 0.5 kpc , tilted by \phi = 44 ^ { \circ } \pm 10 ^ { \circ } to the Sun-Galactic Center line , provides the simplest interpretation of this data .
We examine the possibility that enhanced source counts at l = 26 - 28 ^ { \circ } , 31.5 - 34 ^ { \circ } , and 306 - 309 ^ { \circ } are related to Galactic spiral structure .
Total source counts are depressed in regions where the counts of red objects ( m _ { K } - m _ { [ 8.0 ] } > 3 ) peak .
In these areas , the counts are reduced by extinction due to molecular gas and/or high diffuse backgrounds associated with star formation .