Less formally, it is the intersection of the surface with the plane
perpendicular to *z* at height *c*. For a
closed
surface, the level set will generally be a collection of closed
curves.

As the height passes a critical level the topology of the level set will change, usually by changing the number of components of the level set.

* 8/12/94 dpvc@geom.umn.edu -- *

*The Geometry Center*