Autodesk CIVIL3D - CIVILDESIGNCOMP 2007 SLM CD Tutorials Manual page 74

Breaklines
Breaklines define linear surface features, such as retaining walls, curbs, tops
of ridges, and streams. Breaklines force surface triangulation to run along the
breakline; triangles do not cross a breakline.
Breaklines are critical to creating an accurate surface model. Breaklines are
important because it is the interpolation of the data, not just the data itself,
that determines the shape of the model.
You can use 3D lines or 3D polylines as breaklines. Each vertex on the polyline
is converted to a TIN point with the same XYZ coordinates. For 3D lines, each
line that you select is defined as a two-point breakline.
For more information, see the AutoCAD Civil 3D Help topics Creating Surfaces
and Adding and Editing Surface Data.
62 | Chapter 5 Surfaces Tutorials