Contribution to the HCN(1−0) luminosity of the different H₂ column density bins to which each cloud has been assigned. The vertical dashed line indicates the column density corresponding to A_K = 0.8 mag, proposed by Lada et al. (2010) as the boundary of the cloud dense gas. For the California cloud, no HCN(1−0) emission was detected toward the lowest column density bin, so its contribution to the luminosity has been set to zero (see the main text).