IC1553 line ratio maps. Every map is masked, excluding those bins with S/N < 2 or a relative error of greater than 40% for the respective lines. We overlay the same Hα map of the galactic plane masked in Figure 1. The y-axis is rescaled as a function of the galaxy inclination. In this case, the galactic plane is defined as a rectangle with the minor side equal to the minor axis of the fitted ellipse and the major side extending the full length of the x-axis.