Effect of metallicity on the selection function. Top left: distribution of metal-poor RC-GSP-Spec stars projected the Galactic (X, Y) plane for stars with |Z|< 200 pc alone. The Sun is at (X, Y) = (0, 0), and the Galactic centre is to the right. Top right: same for the most metal-rich stars in the sample. Metal-rich stars contained in the sample reach larger distances from the Sun. Bottom: G magnitude distribution in the entire sample (black) and in four ranges of metallicity. The offset ΔG used in Eq. (9) is indicated for the most metal-poor metallicity group.