1D (top panel) and 2D (bottom panel) N II-BPT diagram, with each point colour coded according to its distance from the extreme starburst line of Kewley et al. (2001, black dashed line in the top panel). The distance (Δ N II), ranges from dark blue for pure SF to red for pure shock or AGN emission. In the top panel, we also show the empirical demarcation line from Kauffmann et al. (2003, black dotted line), indicating a more stringent limit for photoionised gas. In the bottom panel, the black contours correspond to Δ N II = 0 and white dashed lines indicate the position of the bar and spiral arms.