A surface is composed of the following:
Surfaces only use survey points designated as Topo Points. You can designate Topo Points in a number of different ways. Once the surface is drawn, you can even turn off the topo designation for individual points to fix blunders in your surface. To learn more about editing topo points see Editing Topo Points.
TPC generates its surface from a TIN (Triangulated Irregular Network). It creates triangles that model the surface, connecting all the border and topo points then interpolating the elevations along the edges of each triangle. See Creating a TIN.
Breaklines allow you to model grade breaks like ‘top of slope’ and ‘toe of slope’ with a minimal number of points. You can accomplish the same final surface shape without breaklines, but it requires taking numerous points along each breakline. It takes a little practice to gain experience collecting and using breaklines, but the investment is well worth it. See Using Breaklines.
Every surface has a border which constrains the surface. If you think of the surface as a TIN, the border is all the outside edges of all the outside triangles. These are the triangle edges that have just one triangle to the inside and no triangles to the outside.
The border defines the limits of a surface. Only the topo points that lie within the border are used to generate the surface. In this way, the border also affects the shape or 'outline' of the surface.
By default, a surface is constrained to its 'convex border'. Think of this a stretching a rubber-band around all the topo points in the surface. If you don't specify a border for a surface, it defaults to this convex border. This makes creating a surface very simple. See Inserting Surfaces.
You can also select a traverse to defines the border of the surface either when you create the surface or anytime you edit the surface. See Surface Borders.
By default, TPC groups a surfaces drawing objects onto layers. Major contour lines and labels are placed on the TPCContourMajor layer and so on. If you want to change the layers that a surface is placed on, use the Advanced dialog. See Surface Layers.
Surfaces can be optimized to improve drawing speed, reduce memory requirements or allow interactive editing. See Optimizing Surfaces.
TPC collects information about the surfaces it creates to help you correct problems or improve the shape of the surface.