Illustration of the correspondences between ellipses and cusps. Left panels: transverse PV diagrams at δz = 2.9″ and 7.5″ (from Fig C.1), with red dots indicating the on-axis projected velocities of cusps U1 and U2 at δz = 7.5″. Each of these two cusps corresponds in position and velocity to the maximum velocity (back side) of an ellipse in the PV cut. Right panels: channel maps at the same line-of-sight velocity as the orange crosses in the left panels, showing that elliptical structures seem to correspond to fainter cusps in position-position space, but falling outside of the velocity domain where cusp characterization was possible.