Originally Posted by
David Conant
Revit draws contour lines after it triangulates the toposurface. It finds a constant height path across triangles and draws the contour. contour segments When a sub-region is created, Revit re-triangulates so that triangles don't cross the boundary. Since this causes some shift in the triangles, it can also cause some shift in the position of contour lines. The effect will be most noticeable for gentle slopes where a small vertical shift can result in a larger horizontal one. In the surface itself, the change in elevation of any point on the surface due to re-triangulation is never more than an inch or two (2-5cm).