Top: distribution of birth radii R_b of stars currently found in the solar vicinity (grey shaded area in all panels, extending from 7–9 kpc) for stars of different ages (in 1-Gyr wide bins, colour-coded by age), as predicted by our standard (left) and 2-SFB (right) models. Middle: radial metallicity profile of each mono-age population. The blue dots indicate boundaries including 95%-tiles of model local stars in the R_b distributions of the top panel. Bottom: the dashed lines represent the mass weighted (according to the distributions of the top panel) abundance gradient of each mono-age population.