Distribution of stellar mass in the [Mg/Fe] vs. [Fe/H] plane as a function of Galactocentric distance, R, and lzl. The bottom set of panels corresponds to the radial selection only, within 15 kpc from the mid-plane. In each panel, the yellow lines show the normalized [Mg/Fe]- and [Fe/H]-distribution functions, and the white line shows a boundary used to separate high- and low-α populations. The masses of high- and low-α populations in a given radial and vertical bin are marked with the grey numbers in M_⊙ units.