Evolution of the velocity PDF as successive numerical processing steps are applied to one TURB-15 map. The gray histogram shows the H I PDF from S25 (70–500 pc, |v_los| ≤ 40 km s⁻¹). Blue histograms correspond to (A) the intrinsic full-resolution 3D simulation, (B) the 2D (x,y) map obtained by averaging along z, (C) the synthetic sky projection (4 pc radial, 10° angular sampling), and (D) the same projection after applying one observational mask.