Top panel: map of the medians of the Gaia DR2 radial velocities as a function of Galactic coordinates. The Galactic centre is in the middle of the figure and the Galactic longitudes increase to the left. The pixel size is ~ 0.2 square degree (healpix level 7). Bottom panel: face-on view map of the medians (over cells of 200 pc × 200 pc) of the Gaia DR2 radial velocities, Ṽ_R, for the Galactic disc as seen from the north Galactic pole. The Galactic azimuths increase clockwise. They are labelled from − 30° to + 30° on the left of the map. The Sun is represented by a black dot, located at X = −8.34 kpc (Reid et al. 2014) and Y = 0 kpc. The Galactic centre is located on the left side. The Milky Way rotates clockwise. The Galactic longitudes are defined counter-clockwise (around the Sun). The iso-velocity contour Ṽ_R = 0 is pointed out as black lines. The map has been calculated using 5 020 596 stars, selected in a 2 kpc horizontal layer centred on the Galactic mid-plane.