A feature line represents an object in the drawing from which you want to grade, such as a swale or a ridge line.
A feature line is a special type of line that grading commands recognize and use as a footprint.
You can draw feature lines, create them by converting existing objects, or export feature lines from corridors. Surfaces can use a feature line as a breakline. You can select a parcel lot line or feature line as the grading footprint.
Unlike 3D polylines, feature lines support arcs without tessellation. Tessellation is undesirable in a grading footprint because it results in many small grading faces joined by radial corners. To avoid tessellation, you can create a feature line from a 2D polyline with arcs, and then apply elevations using the Grading Elevation Editor. If you want to create a grading from a footprint that has tessellated curves, you can use the Fit Curve command to convert the tessellation to true arcs.