Top: relation between the CO(1−0) intensity (in K km s⁻¹) and the local L_TIR for LOSs where HCO⁺(2−1) has been detected with DeGaS-MC (and associated Pearson correlation coefficient R). The shaded points complement the relation for all LOSs where CO(1−0) has been detected. The colors separate the various star-forming regions and the increasing size of the symbols indicates an increase in the YSO number (0, 1, 2 or 3) for each LOS. The corresponding local SFRs are indicated on the upper x-axis. Middle and bottom: variation of the HCO⁺(2−1)/CO(1−0) (middle), a proxy for the dense gas fraction, and of the HCN(2−1)/CO(1−0) (bottom) ratio (with intensities in K km s⁻¹) as a function of the local L_TIR.