Relation between SFE and the dense gas measures of individual clouds. Light blue shows clouds with a distance > 1.2 kpc. The symbol size corresponds to the cloud area > 3mag. Left: Dense gas mass fraction, f_DG, versus SFE. The line shows a fit with a = 0.6 ± 0.2, similar to the relation found previously for nearby molecular clouds (e.g. Kainulainen et al. 2014). Right: Relative density contrast, ΔA_V, versus SFE. The line shows the fit of SFE ∝ 10^aΔA_V with a = 1.6 ± 0.4.