Mean metallicity along the line of sight as a function of Galactic longitude l and Galactic latitude b for the APOGEE DR13 data (left), model M1 (middle) and model M2 (right). For the observed (theoretical) map only stars (particles) with distances between 4 and 12 kpc from the Sun are selected. Only pixels with more than 10 stars (particles) are shown. Each bin is 2 degrees in l and b. The black contour lines correspond to iso-metallicity contours, as labelled on the colour bar.