Oriented angles of the gradient of column density and centroid velocity, and their differences for five different toy models of the density and velocity fields. All angles are displayed in degree. The white areas on the images show regions where the gradient is too small to reliably compute its orientation. The different colors of the circular probability distribution function (PDF) correspond to the column density thresholds which are used in the Orion B data set analysis: log(N_H) > 21.00 cm⁻² are shown in cyan, log(N_H) > 21.55 cm⁻² in blue, log(N_H) > 22.00 cm⁻² in pink, and log(N_H) > 22.40 cm⁻² in red.