Top-down Galactic map of all clouds with circle sizes indicating cloud masses. Background illustration (Churchwell et al. 2009) produced by Robert Hurt of the Spitzer Science Center, reflecting the current understanding of Galactic structure. The solar circle is drawn in solid purple, and the tangent circle in the inner Galaxy is drawn in dashed purple. The Sun's location is marked with a yellow star and the Galactic Center is marked with a black “x.”