[O iii]/Hβ against [N ii]/Hα relation, one of the BPT diagrams, for the 15 757 extracted emission-line regions in the analysed CALIFA galaxies. Colour scale shows the Hα equivalent width. The solid black line represents the empirical curve from Kauffmann et al. (2003) to divide objects ionised by massive stars and by non-thermal processes. The dashed line is the theoretical curve defined by Kewley et al. (2001). The lower left cross indicates the typical associated error in each axes.