About Creating Surfaces
A surface can be one patch, or it can be composite.
To create a surface, use two or more chains. A chain is composed of curves or edges with tangent continuity between them.
The defining chains of a surface must have soft point connections, or they must share vertices at the endpoints where they intersect.
You can select and trim primary chains or internal curves of a composite surface for defining a surface.
To further define surface shape, you can add internal curves to boundary surfaces and cross curves to sweep surfaces.
Use reparameterization curves to shape boundary or loft surfaces when you create or redefine them.
You can convert a boundary surface into a trimmed rectangle surface and vice versa.
When you make a composite surface into a trimmed rectangle surface, one patch surface is created. You can use automatic curve connections to define the surface.