Column-normalised 2D histogram of stellar birth radius versus final radius at 10 Gyr for the models. Stars here satisfy |z| < 0.3 kpc and λ_c > 0.9. The solid green and dashed red lines reflect the 1 : 1 relation and the location of the age upturn, respectively. While the distribution follows the 1 : 1 line in the inner disc, we find a knee in the distribution near the age upturn. Stars beyond the age upturn were born in the inner disc and subsequently migrated outwards.