A surface is a three-dimensional geometric representation of an area of land, or, in the case of volume surfaces, is a difference or composite between two surface areas. Surfaces are made up of triangles or grids, which are created when Autodesk Civil 3D connects the points that make up the surface data. To use a surface in your drawing, you can create an empty surface and then add data to it. You can also import existing files containing surface information, such as LandXML, TIN , or DEM files. Points or contours are usually a primary part of the original surface information and are supplemented with breaklines and boundaries.