The two-dimensional proper motions of stars with magnitudes G ≤ 16.5 in the field of NGC 188 are displayed. Proper-motion members of NGC 188 are shown in red, while field stars are depicted in gray. Contours in the main panel represent the 1σ, 2σ, and 3σ levels of the Gaussian distribution for the cluster, along with the 0.5σ level for the field’s Gaussian distribution. The top and side panels present the one-dimensional projections of the stellar and Gaussian distributions for the cluster and the field, the latter plotted in red and gray, respectively.