A ____________ breakline is 2D, meaning that it has no elevation data.

• A. Contour
• B. Proximity
• C. Elevation
• D. Reference

Answer: (B)

Breaklines shape how a Civil 3D surface is triangulated, and they can be either 2D or 3D depending on whether the line carries elevation data. A proximity breakline is defined in the plan view only; it has no Z value along the line, so it is 2D. This means it influences the surface based on distance to the feature rather than height, which is exactly what “no elevation data” implies. Contour and Elevation breaklines carry elevation along the line (contour lines have a specific elevation, and an elevation breakline enforces a set height), so they are 3D, not 2D. Reference breaklines are used as references rather than to define height, so they wouldn’t fit the description as cleanly.