[O iii] λ5007/Hβ vs. [N ii] λ6583/Hα diagnostic diagram for the 396 H ii ionized regions detected in NGC 6754, color-coded by the deprojected galactocentric distance (where bluer colors correspond to the central regions, and reddish-to-grey colors correspond to the outer regions). Solid and dashed lines represent, respectively, the Kauffmann et al. (2003) and Kewley et al. (2001) demarcation curves. They are usually invoked to distinguish between classical star-forming objects (below thesolid line), and AGN powered sources (above the dashed line). Regions between both lines are considered intermediate ones. The average error of the line ratios is represented by the error bar in the upper-right corner.