Average Galactic H₂ surface densities of the diffuse (red, detected in ¹²CO, undetected in ¹³CO), dense (green, detected in ¹²CO and ¹³CO), and very dense (blue, detected in ¹²CO, ¹³CO, and CS) components averaged in bins of width 0.1 kpc, as a function of Galactocentric radius in the GRS+UMSB (inner Galaxy only, top), in the EXFC 135–165 survey (outer Galaxy only, middle), and in the EXFC 55–100 survey (inner and outer Galaxy, bottom). In the inner Milky Way covered by the GRS, the pink filled curve indicates the surface density of H₂ in molecular clouds identified with a clump finding algorithm in Roman-Duval et al. (2010).