zonogons are the two-dimensional analogues of three-dimensional zonohedra and higher-dimensional zonotopes. as such, each zonogon can be generated as the minkowski sum of a collection of line segments in the plane. if no two of the generating line segments are parallel, there will be one pair of parallel edges for each line segment. every face of a zonohedron is a zonogon, and every zonogon is the face of at least one zonohedron, the prism over that zonogon. additionally, every planar cross-section through the center of a centrally-symmetric polyhedron (such as a zonohedron) is a zonogon.