The surface modeling tools in Autodesk Civil 3D software include generic ones, such as points and breaklines, as well as purpose-built site grading tools for grading with feature lines and projected slopes. Understanding the strengths and limitations of each tool—and learning how to use them together—is a major part of learning best practices in grading.
Create a set of feature lines to define the graded region as surface breaklines, and then adjust the elevation of key points to control the shape of the surface. Use this grading method for wide, fairly flat areas, such as parking lots or building pads. It is also well suited to areas with rapidly changing elevations or slopes, where walls would normally be required to grade successfully. You can manually add or remove feature lines, and adjust their location in three dimensions, to achieve precise slope design. Using this process, you can control water drainage, or clean up difficult geometry in areas such as the intersection of two or more slopes.
Project a slope from a feature line to an intersection with a surface, or to a specified distance, elevation, or elevation difference. Use this grading method to calculate proposed feature lines based on some criteria. A major benefit of projection grading is that the resulting grading objects remain true to the original criteria if the base feature line is edited. Additionally, you can edit the criteria, and the grading model reflects the change. This method works best when you need to maintain relationships between feature lines.
This section explains some techniques for using each of these tools to get optimal results from Autodesk Civil 3D.