Observed stars (grey points) in the 3D space formed by APOGEE DR16 abundance ratios (i.e. [Fe/H] and [Mg/Fe]) and maximum vertical excursion from the midplane |z_max| (from astroNN catalogue) in the Galactic region between 6 and 10 kpc with |z|< 2 kpc compared with model predictions by ES20 and ES21 (white solid and dashed lines, respectively). The associated projections are drawn with red, blue, and green points (data) and lines (models), respectively. In the left panel all the stellar ages have been considered, while in the right one only observed and predicted stars younger than 8 Gyr have been drawn. In both panels, the colour-coded points indicate the predicted surface stellar mass density ΔM_⋆ formed in constant age intervals fixed at the value of 0.05 Gyr normalised to the maximum value ΔM_⋆, max.