Time evolution of the radial [Fe/H] gradient as predicted by the two-infall model at Age > 3 Gyr (left panel), 1 < Age/Gyr < 3 (central panel), and Age < 1 Gyr (right panel) for the two-infall model, including stellar migration and abundance uncertainties (see Sect. 3.4). Density plots show the normalised density (in log scale) of stars as predicted by the model in given Galactocentric bin of 0.2 kpc width. White contour lines show the limits within are contained the 68% (solid) and the 95% (dashed) of the predicted stellar distribution in a given radial bin. Solid lines show the results for the [Fe/H] gradient as predicted by the genuine chemical tracks, i.e. the ones shown in Fig. 1, at Ages=0.5 Gyr (cyan line), 2 Gyr (green line) and 5 Gyr (magenta line). Data are the same as in Fig. 1