Distribution of effective radius, R_e, and mean effective surface brightness, ⟨μ_e⟩_r, of UDG candidates. Blue circles: Full catalog of 966 candidates. Red circles: 693 candidates meeting the selection criteria (3″ < R_e < 20″, ⟨μ_e⟩_r > 23.8 mag/arcsec²). Black stars: 545 HQ Grade A candidates (see Sect. 5.1). Shaded density contours and axis histograms show the distributions of each sample. Dashed black lines indicate the median values of R_e and ⟨μ_e⟩_r.