Breaklines - Civil 3D

Question
What is a Breakline?

Answer
A Breakline is a line used to connect data representing a distinct surface feature, like a ridge line, edge of pavement, toe of a slope, centreline of a road, or flowline of a ditch or stream. When a breakline is defined, the surface triangulation must first follow the breakline, by placing triangle edges coincident with the breakline segments. This ensures the feature in the model is accurately depicted. Then, the rest of the interpolation is performed based on proximity. Breaklines are typically critical to creating an accurate surface model. It is the interpolation of the data, not just the data itself that determines the shape of the model.