Regions are two-dimensional enclosed areas you create from closed shapes called loops. A loop is a curve or a sequence of connected curves that defines an area on a plane with a boundary that does not intersect itself. Loops can be combinations of lines, lightweight polylines, circles, arcs, ellipses, elliptical arcs, splines, 3D faces, traces, and solids. The objects that make up the loops must either be closed or form closed areas by sharing endpoints with other objects. They must also be coplanar (on the same plane). The loops that make up a region must be defined as an array of objects.
For more information about working with regions, see â€œCreate and Combine Areas (Regions) in the User's Guide.