A simple rotation curve in a flat circular galaxy, and its "spider diagram" -- its 2D isovelocity contour diagram. The galaxy projects to the ellipse (so the line of nodes in this figure is horizontal), and the location of the turnover radius is the inner oval. In the solid body part of the rotation, the velocity contours are parallel and spaced in proportion to the velocity gradient. Outside, the approximately flat rotation curve leads to radial contours, but because the rotation curve turns over and falls, the contours close along the major axis. Notice the kinematic major and minor axes (lines of symmetry of the velocity contours) are aligned with the photometric major and minor axes.