Hey everybody. Welcome back to the channel. In this video, we’re going to get a brief introduction into the world of surfaces in Civil 3D. Now, specifically, we’re going to dive into the definitions of different elements involved with creating them, elements such as tin surfaces, contours, brake lines, and boundary data. Now, in upcoming tutorials, we’re going to explore how to create these elements in future videos.

Now, in this example, you’ll see three different aspects to our surface. You’ll see these little pluses right here, which represent our point data. You’ll see all of these lines connecting our point data and those are what’s known as tin lines. And then, those tin lines are what create our surface contours. So, let’s dive into that a little bit more.

Now, the reason why we have so many points out here is mainly due to the fact that this looks like a mountain that was actually shot out here and you can’t necessarily get a field crew to shoot individual points with a rod, of course, on a mountain. So, what they did is they probably used a drone with LIDAR. And what LIDAR does is it actually creates all of these points as it’s flying over it. So, you can get a drone to go out and go just back and forth across the site, and collect all of these different points as it’s flying around.

In this example, all of our point data was entered in directly into the drawing as opposed to importing them with the survey database like we’ve done in the past. So, all of these points are just housed within our drawing. If we click on our prospector, you’ll see under surfaces, we have an existing surface and the surface is defined by a point text file that we brought into the drawing. Everything, again, is all housed within the drawing itself.

When we zoom in on our point data, you’ll see that each point is connected to each other, and these lines are what they call tin lines. Now, all of these tin lines create triangles between each of these point vertices. And in doing that, Civil 3D does what’s known as interpolation. The grade is calculated between each of these points, and that’s what helps to develop our surface contours.

In this example, again, we created our contours based upon point data that we inputted into the drawing, but you don’t necessarily have to go that route. Instead, you can always bring in 2D or 3D pie lines and, just so long is those lines have X, Y, and Z coordinate data, you can add them into your surface by clicking on contours and clicking add.

Now, there are two different types of boundaries. There are destructive and non-destructive, and what these boundaries are used for is to encapsulate our surface. Say, for example, we don’t want to include all of this triangulation in between these areas right here. This could be, say, a lake or it could just be an area that we don’t want to include maybe in our surface volume.

So, what a boundary will do is it won’t include this triangulation. Now, the difference between destructive and non-destructive is that, if it’s destructive, then it’ll chop out all of these tin lines in between. But non-destructive, it’ll include all of these tin lines. It just won’t include them within, say, a volume calculation.

We can also use the same concept to create an inner boundary as well. So, we’ve got our outer boundary and we can also have an inner boundary, say, for an existing detention pond that we would like to omit all of this information from our volumes.

Lastly, I want to introduce you to the concept of brake lines. Now, say, for example, there was an existing wall that was right along this area right here. Now, with a brake line, we don’t want triangulation to cross our wall. If our tin lines cross our wall, it would create an inaccurate surface because it’s not accounting for our wall itself. So, say, for example, if this was a retaining wall, a three foot retaining wall creates an obvious grade change, which our tin lines are not accounting for. So, brake lines account for that.

If you’d like to learn more about Civil 3D workflow tips and tricks, visit, and be sure to sign up for future video notifications or click subscribe on our YouTube channel. Again, my name is Charles Ellison. Take care.


This tutorial demonstrates how to create a TIN surface, and then add contour, breakline, and boundary data to the surface.

When you create a surface, its name is displayed in the Surfaces collection in Toolspace on the Prospector tab. From this location, you can perform other operations, such as adding data and editing the surface. When first created, the surface is empty, so it is not visible in the drawing.

After data has been added to a surface, it becomes visible in the drawing in accordance with the display settings specified in the referenced surface style.

TIN Surfaces

A TIN surface is composed of the triangles that form a triangulated irregular network. A TIN line is one of the lines that makes up the surface triangulation.

To create TIN lines, Autodesk Civil 3D connects the surface points that are closest together. The TIN lines form triangles. The elevation of any point in the surface is defined by interpolating the elevations of the vertices of the triangles that the point lies in.

TIN surface with contour lines displayed

Contour Data

Contours are graphical illustrations of surface elevation changes. You can create a surface from contours drawn as 2D or 3D polylines that have x, y, and z coordinate data.


Boundaries are closed polylines that affect the visibility of the triangles either inside or outside the polylines. An outer boundary defines the extents of the surface. All triangles inside the boundary are visible, and all triangles that are outside the boundary are invisible.

Areas hidden by boundaries are not included in calculations, such as total area and volume.

Surface boundaries are defined by selecting existing polygons in the drawing. The surface definition displays the numerical ID and a list of vertices for each boundary.

A surface before adding a non-destructive outer boundary

The effects of a non-destructive outer boundary


Breaklines define linear surface features, such as retaining walls, curbs, tops of ridges, and streams. Breaklines force surface triangulation to run along the breakline; triangles do not cross a breakline.

Breaklines are critical to creating an accurate surface model. Breaklines are important because it is the interpolation of the data, not just the data itself, that determines the shape of the model.

You can use 3D lines or 3D polylines as breaklines. Each vertex on the polyline is converted to a TIN point with the same XYZ coordinates. For 3D lines, each line that you select is defined as a two-point breakline.

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