Simplified illustration of the map processing, on N = 9 concentric circles, with radii regularly spaced between R_min = 0 and R_max = 0.8 kpc. Top panel: Velocity map overlaid by the concentric circles (in gray dotted lines). The red dots (resp. blue triangles) are the maximal (resp. minimal) values V_max (resp. V_min) for each circle, and have been computed with n = 7. Bottom panel: Previous extrema V_max and V_min of the velocity displayed as a function of the distance from the center (i.e., the radius of its corresponding circle). The negative distances corresponds to the blue shifted part of the map, where the velocities are negative. The gray lines represent the origin axes.