Face-on maps of the mean stellar metallicity [Fe/H] distribution across the MW disc. From left to right, the maps represent stellar populations within horizontal slabs at increasing distances from the midplane. Near the midplane (two panels on left), the bulge region appears to be metal-poor because of the deficit of the metal-rich (low-α) populations expelled to higher distances perpendicular to the disc plane via bar/bulge instability. However, the actual metallicity of the MW bulge is higher compared to the surrounding disc once its full vertical extension is taken into account. The bar appears to be metal-rich along the major axis because kinematically colder low-α (metal-rich) populations are more efficiently captured by the bar’s gravitational potential compared to the hotter high-α (metal-poor) stars dominating along the bar minor axis.