Diagnostic diagram showing log([O iii]λλ5007,4959/Hβ) versus log([N ii]λ6584/Hα) for models computed with SAL2 IMF. Each shell shows a different metallicity model and the corresponding data in that metallicity range. Symbols have the same meaning as that in Fig. 9 with the addition of blue dots which correspond to H ii regions from Yin et al. (2007).