This figure illustrates a topology before several attempted movements of node N1. The text after the illustration explains whether or not the operation would be allowed for each attempted move of node N1 to points P1, P2, P3, and P4.
The topology includes a polygon and point P4, which is outside the polygon. Edges E3 and E1 go across the polygon, dividing it into faces F1 (above) and F2 (below), and these edges meet at node N1. Points P1 and P2 are on face F1, point P3 and isolated node N2 are on face F2, and point P4 is outside the polygon. Edge E2 extends from node N1 into face F1, edge E4 extends from node N1 into face F2, and edge E5 extends from an unspecified point on the perimeter of the polygon into face F1.