Density plot in logarithmic scale showing the VVV bulge area. The map was made using the multi-band JHK_s CASU v1.1 and v1.2 catalogues for point sources brighter than K_s = 16.5 mag (see text). Crowded areas appear in yellow, while less populated regions as well as highly extincted areas are shown in blue. The overlapping regions between the tiles are highlighted since the point sources are accounted for twice. Dashed lines mark the 15 areas selected to build the colour–magnitude diagrams shown in Fig. 6 (see Sect. 4). The source density, in units of 10⁵ sources deg^-2, is indicated in the horizontal bar at the top.