Top panels: W80_[NII] against log([N II]/)Hα, log([S II]/)Hα, and log([O I]/)Hα, from left to right, obtained from the fitted total line profiles. The plotted measurements are colour-coded from purple to red, going from low to high flux ratios and line widths. Dashed and solid lines represent shock model grids from MAPPING V (Sutherland & Dopita 2017; Sutherland et al. 2018). Each line connects predicted line ratios of a certain metallicity (1 Z_⊙, solid lines; 2 Z_⊙, dashed lines), pre-shock electron density (1 cm⁻³), and magnetic field (from 1 to 10 μG, as labelled in the first panel for 2-Z_⊙ models), with changing shock velocities V_s in the range 200 − 1000 km s⁻¹. We assumed a one-to-one correlation between V_s and W80. Bottom panels: Arp220 maps associated with the top panel diagrams, using the same colour codes.