Correlation between 24 μm fluxes and 21 cm fluxes for the W31 complex. Only pixels with 24 μm flux above 120 MJy sr^-1 (corresponding to the approximate outskirts of the Hii regions) and 21 cm emission above the 3σ level of  ~ 0.01Jy beam^-1 are plotted. Furthermore, only correlations on scales of the beam size of the 21 cm observation were used (2-pixel steps corresponding to 29′′).