Dense gas measures of clouds as a function of galactocentric radius (blue circles). Clouds with R_Gal < 7.5 kpc are shown in lighter blue, and size corresponds to the cloud area. Top: mean surface density of the individual clouds as afunction of the galactocentric radius. The green crosses show the data points from Miville-Deschênes et al. (2017), and the red diamonds shows the data from Roman-Duval et al. (2010). Middle: dense gas mass fraction, f_DG, as a functionof the galactocentric radius. Bottom: density contrast, ΔA_V, as a function of the galactocentric radius.