Panel a: symbols show the excitation parameter P as a functionof the N₂ line intensityfor the spaxels in central regions (R_g < 0.1) of several MaNGA galaxies. The mean values of P for objects in bins of 0.1 dex in logN₂ are presented. The solid line shows the excitation parameter P as a functionof N₂ for the H II regions in the nearby galaxies with 0.03 > log(O/H)_N – log(O/H)_R > −0.03. The long-dashed line shows P for H II regions with 0.09 > log(O/H)_N – log(O/H)_R > 0.03, and the short-dashed line shows P for H II regions with − 0.03 > log(O/H)_N – log(O/H)_R > −0.09. Panel b: same as panel a but for the N₂/R₂ line ratio. Panel c shows the same as panel a but for spaxels with galactocentric distances from 0.775 to 0.825 R_g. Panel d shows the same as panel b but for spaxels with galactocentric distances from 0.775 to 0.825 R_g.