Stellar colours for Galactic direction (l, b) = (10°, 20°) for a sample of stars simulated from the Besançon model (Robin et al. 2014). The different intervals of J-band magnitude are plotted in different colours, as indicated by the values in the upper part of the figure. After the first one (8.0–11.0 mag), the subsequent sets of points are shifted by Δ(H−K) = 0.15 mag, for better readability. The smoothed contours are drawn at 10% and 50% of the maximum star density.