Comparison between the maximum volume densities obtained for the clouds in our sample at the fixed angular resolution of 36.3″ provided by the Herschel telescope, and at the fixed spatial resolution of 0.1 pc used by Kainulainen et al. (2014). The 12 clouds in common between the Kainulainen et al. (2014) sample and ours are highlighted by square markers. The bottom panel is a zoom-in of the area defined by the horizontal dashed lines in the top panel, at the very low SFE relevant for defining a star formation threshold.