Mean radial velocity (two leftmost panels) or velocity dispersion (two rightmost panels) values as a function of longitude, at a fixed latitude, compared to a surface cut at the same latitude. Data for a given latitude are shown with the same color of the curve at that latitude. Black dots were not included in the fits, for the reasons explained in Sect. 4.2. Points at b =  +4.5 are shown here together with the curve at |b| = 4.5 in order to verify the assumption of symmetry about the Galactic plane.