Cold dust effective temperature vs. deprojected galactocentric distances for the 140 of our GDCs with temperature measurements. 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 blue filled circles (CO detections), yellow unfilled squares (marginal CO detections), and red crosses (no CO detections). The vertical error bar in the lower left indicates the uncertainty in temperature that we assume for all GDCs. The dashed line is a fit through the data points and has a slope of − 1.3 ± 0.1. The shaded region indicates the typical temperature uncertainty interval of ±1.5 K.