Maps of the higher order moments of the longitudinal (odd columns) and latitudinal (even columns) proper motions. The two left (right) columns correspond to the barred (axisymmetric) model. We apply the restriction |Z| < 1 kpc to ensure that all the particles lie in the disc. The bar and the galactic centre are represented by the solid black line and the black spot, respectively. Open circles enclose the regions whose distributions are described in Sect. 4. Values above (below) the limits of the colour bar, if present, are shown in dark (light) grey.