Histograms from Arenou et al. (2018) of source pair separations in two circular test fields for Gaia DR2 sources (red lines); Gaia DR2 sources with G_BP and G_RP photometry (blue lines); and Gaia DR1 sources (black lines). Top: a dense field of radius 0.5° at (ℓ, b) = (−30°, −4°) with 456 142 sources, bottom: a sparse field of radius 5° at (ℓ, b) = (−100°, −60°) with 250 092 sources. The thin, dotted lines show the relations for a constant density across the field.