Mean LSR velocity at height $z=z_0^{\mathrm{\prime }}$, defined as the z coordinate corresponding to the maximum gas density at each x and y position, smoothed with a Gaussian filter with a 50 pc width. The markers are akin to Fig. 5 but consist of two parts: The inner part shows the measurement value and the outer part shows the mean value of the reconstructed velocity fields at the position of the tracer object. Markers with a thick grey edge indicate tracers whose radial velocity component is badly reproduced by the reconstructed velocity field.