Density map on the XY Galactic plane (i.e., computed at Z = 0) for a spiral perturbation with f = 0.3 (used as a reference model). The Sun is located at X = −8.178 kpc and Y = 0. The different colored lines present the different spiral arm models according to Reid et al. (2019): in dark green is the Outer arm, in blue Perseus arm, in black the Local arm, in cyan the Sagittarius-Carina arm, and in lime the Scutum arm. In the inset, we show a zoomed-in image of the Perseus region.