Regions are two-dimensional areas you create from closed shapes or loops. Closed polylines, lines, and curves are valid selections. Curves include circular arcs, circles, elliptical arcs, ellipses, and splines.
Closed 2D and exploded planar 3D polylines in the selection set are converted to separate regions and then converts polylines, lines, and curves to form closed planar loops (outer boundaries and holes of a region). If more than two curves share an endpoint, the resulting region might be arbitrary.
If a selected polyline has been smoothed by either the Spline or Fit option of , the resulting region contains the line or arc geometry of the smoothed polyline. The polyline is not converted to a spline object.
REGION deletes the original objects after converting them to regions unless the system variable is set to 0. If the original objects were hatched, hatch associativity is lost. To restore associativity, rehatch the region.