Edit surface data for greater accuracy.
As surface triangles are created around contour data, erroneous flat triangles can appear in regions where contour lines follow tight curves, creating a condition where all three points of a triangle can be on the same contour. When you add contour data to a surface, it is important to understand how to use the settings for minimizing flat areas. Otherwise, the minimizing operation can run very slowly, and the resulting surface can be inaccurate.
Figure 6: Default settings when adding contour data
If you add all your contour data in a single operation, use the three default settings shown in figure 6 to edit the contours and create a more accurate surface. AutoCAD Civil 3D uses these options to correct flat areas by checking the surrounding elevations, interpolating new points, and subdividing triangles.
If you add contour data in two or more batches, clear the check boxes for the initial batches, so that contours are not edited based on incomplete data. When you add the final batch of contour data, select the three check boxes to correct the contours based on the full data set.