Comparison of the original intensity spatial distribution (top row) with the mean intensity computed for each cluster separately (bottom row). The colour scales are identical for the top and bottom rows, but they differ from one column to another. The levels shown on the bottom colour lookup table represents the mean values of the cluster intensities. The clusters were defined using the ¹²CO, ¹³CO, and C¹⁸O (1–0) lines. The circles show the typical extensions of the Hii regions and the crosses show the position of the associated exciting stars (see Pety et al. 2017, for details).