Two colour–colour diagrams involving Hα: in the top panel, r_I − Hα vs. g − i and in the bottom panel, r_I − Hα vs. r_I − i, both shown for the Galactic longitude range, 60° < ℓ < 65°. As in Fig. 14, the density of catalogued sources is portrayed by the squared root contoured colours. Only sources with r_I <  19 mag and errBits = 0 have been plotted. The solid line in red is the unreddened main sequence, while the dashed line is the reddening line for an A2V star up to A_V = 10. The blue line is the sequence for the giants. The grey dashed line is the emitters selection cut appropriate to these longitudes, applied within the range −0.3 <  r_I − i <  2.5, while the grey dots are the selected emitters at > 5σ. The emitter selection is presented in Sect. 9.1.