Left: distributions of HII regions, GMCs, and 6.7 GHz methanol masers projected into the Galactic plane. The symbols are the same as those in Fig. 2. The kinematic distances are estimated using the rotation curve of BB93. Right: color intensity map of spiral tracers. The IAU standard R₀ = 8.5 kpc and Θ₀ = 220 km s^-1 and standard solar motions are adopted in deriving the kinematic distances if no photometric or trigonometric distance is available.