Mosaic of face-on maps of the median radial velocity, Ṽ_R, of the giant sample. Each map corresponds to a Z layer of 400 pc height, from [+1400, +1800] pc (top left) to [−1800, −1400] pc (bottom right). In each map, the azimuths increase clockwise. They are labelled from − 30 to + 30 degrees on the left of the maps. The Sun is represented by a black dot at X = −8.34 kpc and Y = 0 kpc. The Galactic centre is located on the left side. The Milky Way rotates clockwise. The iso-velocity contours Ṽ _R = 0 km s^-1 are pointed out as black lines. The numbers of stars used to produce the maps are given in the lower left corners.