Color maps showing the distribution of the emission line ratios between [NII]λ6583 and Hα, in a color–magnitude diagram similar to that of Fig. 21. In the present case the solid contours show the intensity of the Hα emission, adopting the same levels as in Fig. 21. The dashed blue contours show 3 intensity levels of the continuum emission at  ~6550 Å (starting at 3 × 10^-16 erg s^-1 cm^-2 arcsec^-2). They have been included to indicate the physical extent of the continuum emission in the galaxies.