Dependence of the number of clumps on distance for SINGS galaxies NGC 2976, NGC 3938, NGC 0024, NGC 0337, and NGC 1512, with lines coloured by the original seeing (FWHM) of the galaxy. The change in the number of clumps has a strong negative correlation (median R² = 0.983) with increased distance. When considering all five galaxies simultaneously, we find a slope of −1.35 ± 0.07 (black dashed line). This suggests that Hα clumps are hierarchical (fractal) in nature, with D ∼ 1.3 − 1.4 (see Sect. 6).