Rotation velocity (top panel), velocity dispersion (central panel) and midplane volume density (bottom panel) profiles for our fiducial H I disc model of the Milky Way. Profiles for QI and QIV are shown in red and blue, respectively. In the central and bottom panels, solid lines represent the first low-velocity dispersion component, while dashed lines represent the second component at high-velocity dispersion. The top panel shows both the single best-fit values (points with error-bars) and the profile derived by smoothing the latter at 0.2 kpc of resolution (see text). For the sake of clarity, only the smoothed profiles are shown in the other panels. The thick solid black lines represent the averaged smoothed profiles (computed via Eq. (7) for σ and Eq. (8) for n₀).