PARALLEL line method:It is USED for development of prisms and single curved surfaces like CYLINDERS in which the edges and generation of lateral surfaces is parallel to one another.Radial line method:This method is used for pyramids and single curved surfaces like cones in which the apex is taken as a center and its slant edges or generator as the radius for its development.Triangulation method:It is employed for the development of transition pieces.Approximate method:It is used for double-curved surfaces such as sphere because theoretically, it is impossible to develop. Thus, the surface of the sphere is DEVELOPED by the approximate method. In this case when the surface is cut by a number of cutting planes the cut surface is called a ZONE.