Our sample of 74 MATLAS UDGs, selected with a cut of ⟨μ_e, g⟩> 23.3 mag arcsec⁻² and R_e > 1.0 kpc observed with HST (black empty circles), overlaid on the MATLAS dwarfs of Habas et al. (2020) (empty pale blue circles) and UDGs of Marleau et al. (2021) (filled blue circles). Also shown are the dwarfs identified in the Euclid Early Release Observations of the Perseus cluster (grey diamonds; Marleau et al. 2024), Next Generation Virgo Cluster Survey (grey triangles; Ferrarese et al. 2020) and Next Generation Fornax Survey (inverted grey triangles; Eigenthaler et al. 2018) images, as well as Local Group dwarfs (rotated left grey triangles; McConnachie 2012) and Local Volume (rotated right grey triangles; Carlsten et al. 2020). The UDGs found in the Coma (grey cross symbols; van Dokkum et al. 2015) and Virgo cluster (grey plus symbols; Lim et al. 2020) are shown separately. For comparison, we have also included ultra-faint dwarfs (UFDs; grey stars; Simon 2019) and massive ellipticals from the Carnegie-Irvine catalogue (grey large cross symbols; Ho et al. 2011).