Relation between the PDR proportion and the ratio [C ii]/([C ii]+[O i]), for all of the pixels in all of the regions studied here, with the same region color code as in Fig. 1. The 1% and 10% c_PDR values are indicated by the two dashed horizontal lines. The vertical gray line separates regions where cooling is dominated by [C ii] (right) and regions where the cooling is dominated by [O i] (left).