Schematic representation of the hypothesis of an anisotropic and isothermal distribution of an unbiased sample of thick disk velocities superimposed on a thin disk sample. The observer is located at the Sun’s position R_⊙ at the centre. The Galactic centre (GC) is at the bottom of the figure. The directions on the celestial sphere to each star s_i are indicated with dashed arrows for thick disk stars and solid arrows for the thin disk stars. The green thick arrows represent the radial velocities of the thick disk, whose corresponding unknown true velocity vector is in light blue. The thin disk radial velocities are represented by the thin green arrows, and the corresponding unknown olive-green arrows represent the true velocity vectors. Note that the olive-green arrows are generally longer in the GC direction and shorter in the anti-Galactic centre direction as expected from the velocity dispersion trend.