Velocity–distance plot of Hi-GAL sources in regions from Zucker et al. (2020) for sources in quadrants 1 and 2 (a) and in quadrants 2 and 4 (b), respectively. The velocity (±5 km s⁻¹) and the distance (and its uncertainty) of the sight lines as listed in Zucker et al. (2020) are plotted in black. In panel a the Hi-GAL sources are plotted in red (for W3 and Gem_OB1), blue (for W5 and L1293), and green (for W5, CMa_OB1 and RCW38). In panel b the Hi-GAL sources are plotted in red (for Carina, North America, and M20), blue (for Cygnus X), and green (for IC 2944 and M17).