Specific frequency S_N as a function of absolute magnitude for the 74 UDGs in our sample. Top: UDGs with N_GC > 0 are shown as squares with colours that scale with the value of the background and completeness corrected GC count, N_GC. The UDGs with N_GC ≤ 0 are shown as small black circles. Bottom: same as the top but now showing the local density parameter, log(ρ₁₀), in the colour bar. In both plots, the specific frequency of the Coma cluster UDGs (Lim et al. 2018; light green symbols), Virgo cluster UDGs (Lim et al. 2020; light blue symbols), and Perseus cluster UDGs (Marleau et al. 2024; light red symbols) are also plotted. The light grey dashed lines correspond to S_N with a constant N_GC of 1, 10, 20, ..., 90, 100. The error bars are not shown since they are quite large and can be found in Table A.1. The inset plots display the S_N values using a logarithmic scale.