BSpline curves are defined through a control polygon specified through a set of control points.

Two or more control polygons are needed to create a bspline curve. The definition of the curve is determined by the "smoothness" of the geometry, the order, and the number of polygons. For example, a curve created by two control polygons has a maximum order of two and is displayed as a straight line. Curves with three control polygons can have an order of either two or three. If a curve has an order of three, then it is displayed as a curve.

The maximum degree of order for a bspline curve is equal to the number of control polygons; the greatest value of order defines the "smoothness" of the curve.