Total flux at 250 μm vs. extinction-corrected Hα emission for 134 of our GDCs with reliable flux measurements (S∕N > 3) at both wavelengths. The coloured symbols all indicate GDCs that are associated with D88 HII regions. The GDCs that also coincide with regions that were observed by APEX (see Sect. 4.7) are indicated by the blue filled circles (CO detections), yellow unfilled squares (marginal CO detections), and red crosses (no CO detections). The dashed line shows a fit through the GDCs associated with D88 HII regions (orthogonal distance regression also taking the error bars into account); the slope of this fit is 2.4 ± 0.3.