Complete process for defining the S-L line in the [N II] BPT diagrams using the method proposed in Kewley et al. (2006). (a) shows the result of defining the S-L line in the [N II] BPT diagram using the method proposed in Kewley et al. (2006). The huge green asterisk represents the empirical base point. The boundaries of sector ring[9] are marked in cyan. The solid red line is the Ke01 line. The contour filled with bluish colors represents the results for the sample of our collected galaxies. The corresponding number densities of the different colors are shown in the colorbar on the right side of the panel. (b) shows the dependence of the percentage of galaxies count within each Ke-bin in sector ring[9] relative to the total count of galaxies in the entire sector ring on the angle with the X-axis.