l − v slices at b =  +15° (top) and b = −15° (bottom) at longitudes −90° < l < 90°. First column: the best model shown in Fig. 6; second column: the model refined including a radial dependence of dv_φ/d |z|  for R < 4.5   kpc; third column: the model refined including a linear decrease of the halo thickness for R < R_⊙; fourth column: the LAB data. Each datacube is smoothed to 8° resolution. Contour levels in brightness temperature from 0.04   K to 81.92   K scaling by a factor 2.