Comparison of diagnostic emission-line ratios after Baldwin et al. (1981), as obtained within a 3^′′ aperture (small circles; method a), connected by dotted lines with determinations from method b (mean ratios within R_B from radial [OIII]/Hβ and [NII]/Hα profiles; big circles). Data based on method c (luminosity-weighted determinations using integral [OIII]5007, Hβ, [NII]6584 and Hα line fluxes within R_B) and error bars are omitted for the sake of better visibility.The loci of Seyfert, LINERs and Composites, and that corresponding to photoionization by SF are demarcated following Kauffmann et al. (2003b, dashed-dotted curve), Kewley et al. (2001, solid curve) and Schawinski et al. (2007, dashed line).