Same as Figure 10, but now compared to different curves, plotted for visual reference. The dashed-dotted and solid black lines show a leading spiral curve with pitch angles −15° and −7.5°, respectively (see text for more details). The black dotted line shows a circle (pitch angle 0°) at constant radius R=12.3 kpc. In the right panel, the Perseus arm from Drimmel et al. (2024) (grey line) is also shown for reference.