Position-velocity diagrams of the line ratios used to infer the gas physical conditions in the jet: the [Sii]λ6731/6716 ratio increases with electron density, n_e(top left); the [Nii]/[Oi]ratio mainly depends on the ionisation fraction, x_e, and increases for increasing x_e(top right); the [Sii]/Hαratio is decreasing for increasing excitation conditions (bottom left); the [Oi]/[Sii]ratio depends on all the parameters, but is mainly increasing with increasing temperature, T_e, and density n_e(bottom right). To better visualize the variations of the line ratios a histogram equivalent colour scale is used.