(Left) When plague is present in a PSQ (blue square) at for example t = 10, it may spread to one or more of the eight neighbouring PSQs (shown with arrows). In the analysis, spread on the axes NWSE and WE (violet squares) was combined, and contrasted with spread on the perpendicular axes, NESW and NS (grey squares). An analysis with the other possible combination, i.e. NWSE + NS vs. NESW + WE, was also performed. The inset on the right shows all PSQs used in the model.