Kernel density estimates for the distribution of different kinds of galaxies in the n_r − R_e plane. ETGs and LTGs are plotted in the left and right panels, respectively. Different colours indicate different morphologies and star-forming activities (as described in the insets in each panel). The median values of each subset are indicated by ‘+’ symbols. The dashed grey line and the dashed-dotted line are from D’Onofrio (2001) and Graham (2013), respectively (see the text for details).