Distribution of NUV-selected multi-scale stellar associations connected with the HST Nebula Catalogue (see Sect. 3.6). We show the histogram and the cumulative distribution for the stellar association masses (main panel) and ages (inset panel) as solid filled and dashed lines, respectively. Distributions are shown for stellar associations identified at scales of 8, 16, 32, and 64 pc (see Larson et al. 2023), including H II regions with both single and multiple associations. The 8 pc scale is not available for galaxies with distances larger than 18 Mpc (see Table B.1). Here, the ‘scale’ refers to the Gaussian-smoothing lengths used in the multi-scale watershed segmentation of Larson et al. (2023), and should not be confused with the physical radii of the H II regions measured in this work.