You can use Grid to create a cross section surface by chaining (with Manual or Auto) four boundary curves that describe the edges of the surface. When the chaining is completed, the Method dialog box will be displayed giving you two methods of blending the adjacent curves.
Method
Linear
The Linear method of blending produces a surface with a linear transition between the curves.
Bicubic
The Bicubic method of blending produces a surface with a splined cubic transition between the curves and has more curvature than the Linear blend.