Top: the four HSC regions color-coded by the i-band S/N of sources at 24<i<25. Only sources imaged in all six bands are shown. Several masks were applied to rid the catalogs of stellar sources. The dark red circles in COSMOS and XMM are the two UDFs. The gray dots mark the position of sources with known redshifts at i<25. Bottom: their distributions in the i-band magnitude (MAG)-redshift space. NSPEC is the number of galaxies with spectroscopic redshifts. NC2020 is the number of galaxies with redshifts from the COSMOS2020 photometric redshift catalog (introduced in Section 2.2).