Face-on map of the median radial velocity (in km s^-1) for the mid-plane layer ([−200, +200] pc), derived using the giant sample. The two-arm model of Drimmel (2000), adjusted on near infra-red data, is over-plotted as thick black lines. The thick dashed line highlights the locus of minimum density between the two arms. The spiral arms model of Reid et al. (2014) is also over-plotted, i.e. from the inner to the outer disc: Scutum (cyan), Sagittarius (magenta), Local Arm (blue), Perseus (black), and the Outer Arm (red).