Electron temperature as function of Hα surface brightness for each Voronoi bin in Fig. 13. Points are labelled according to whether the corresponding Voronoi bin is part of an HII region (purple circles), the DIG (green diamonds) or of a region ionised by another source (grey stars). Bins with a relative error on the [SIII] line ratio > 30% have been excluded, as wells as bins with T_e >  18000 (spurious detections on the edge of the FoV).