Metallicity distribution for RGB samples from Zoccali et al. (2008) in fields at l = 0° and b =  −4°, –6°, and –12°, and for the red clump samples from Hill et al. (2011) in Baade’s window (columns from left to right). Top: the observed data (green dots with Poisson noise) are compared with model simulations, applying the same selection function as in the observations (red solid lines). Bottom: decomposition in populations of the model simulation. Red solid line: total; green long dash: disc, short dash blue: boxy bar; dotted magenta: thick bulge. The error bars take only the Poisson noise into account and not the observational errors or the metallicity or the error in the selection function estimation.