Contours in Civil 3D: from Google Earth and satellite elevation models to your survey, step by step

Google Earth Pro shows the elevation under the cursor, but it doesn't export contour lines or terrain. There's no button to download the terrain of an area.

Civil 3D once had a command to import a Google Earth surface, but current versions no longer include it. That's why so many tutorials end in paid software like Global Mapper, or in add-ins.

What works: an open digital elevation model. Public terrain data you can download:

• USGS 3DEP (US): 10 m resolution nationwide outside Alaska, 3 m in select areas, and 1 m lidar-derived DEMs across much of the country, from The National Map.
• SRTM (NASA): nearly global at about 30 m, free from USGS EarthExplorer.
• Copernicus GLO-30 (EU Copernicus programme) and ALOS AW3D30 (JAXA): other global 30 m options.

About accuracy. It depends on the source: 3DEP data in the US is far better than SRTM, whose specified vertical accuracy is ±16 m. Use satellite-based contours for planning — site selection, feasibility, preliminary alignments — not for final design or earthwork quantities. That needs a survey.

If you downloaded an elevation file (a 3DEP or SRTM GeoTIFF, for example), Civil 3D turns it into a surface directly.

1. Set the drawing coordinate system. In Drawing Settings, Units and Zone, pick the system for your project: a UTM zone (for example UTM84-10N in San Francisco) or your State Plane zone.
2. Create an empty TIN surface in Prospector.
3. Add the elevation file. In the surface definition, DEM Files, Add. Civil 3D accepts .dem (USGS), GeoTIFF (.tif), ESRI ASCII Grid (.asc or .txt) and ESRI binary grid (.adf).
4. Specify the file's coordinate system. If the model is in latitude and longitude, assign that system: Civil 3D transforms it to the drawing system when it builds the surface. Skip this and the surface lands somewhere else on the planet.
5. Clip the area. Elevation models come in large tiles. Add a boundary to keep only the project area: the surface gets lighter and faster to display.

A regular point grid is the simplest way to bring an elevation model into Civil 3D, and it's what our generator delivers.

1. Import the points: Insert tab, Points from File, PNEZD (comma delimited) format. If the file won't load, see Civil 3D import points from CSV or Excel.
2. Create a point group with them. If the file includes a description (EG, existing ground), you can filter by it.
3. Add the group to the surface: in the surface definition, Point Groups, Add.
4. Set the style with the contours you need (see step 5).

Why points beat the contour DXF: with points, Civil 3D rebuilds the terrain and you control the interval, the style and the labels. The contour DXF is handy if you only need the linework or work in plain AutoCAD.

For design, the surface comes from the survey: total station, GNSS, drone or lidar. The order matters:

1. Import the points with their field codes (EG, EP for edge of pavement, CL, and so on).
2. Build point groups by code. That's how you decide which points belong in the ground surface and which don't, like structures or trees.
3. Add the breaklines. Edges of pavement, ditches, walls, creek bottoms: the polylines or feature lines the terrain must respect. Without them, Civil 3D connects points across a wall or a channel and the contours lie.
4. Add the outer boundary. It removes the long triangles that form at the edges, outside the surveyed area.
5. Check the triangles before the contours. A point at elevation 0, a duplicate point or a mistyped code shows up immediately in the triangle view.

Contours are one way of displaying the surface, and they're controlled in its style:

• Minor and major intervals. For example, 1 ft and 5 ft on a site survey; 20 m and 100 m with a satellite model in hilly terrain.
• Rule of thumb: aim for about 20 contours across the area. Divide the relief by 20 and round to a clean interval.
• Smoothing. It improves the drawing, not the accuracy: it doesn't add information the survey doesn't have.
• Labels. With multiple contour labels, you draw a line across the contours and Civil 3D labels each one it crosses.

Civil 3D doesn't show the contours. Three frequent causes: the surface style has contours turned off (it shows only the border or the triangles); the surface is empty because the definition wasn't rebuilt; or the interval is so small relative to the relief that the contours merge into a solid blob.

The surface shows up somewhere else, or at sea. The drawing coordinate system doesn't match the data: latitude and longitude points in a UTM or State Plane drawing, or the wrong zone or hemisphere.

Long triangles at the edges. The outer boundary is missing, or the maximum triangle length should be limited in the build options.

Impossible spikes or pits. Points at elevation 0, duplicate points with different elevations, or unexcluded voids in the elevation model.

Jagged contours. The interval is too fine for the data resolution, or breaklines are missing along edges and channels.

If your office builds surfaces every week, the procedure never changes: import points with the same codes, create the same groups, add breaklines by code, apply company styles and label. That's exactly the kind of task worth automating.

• With Dynamo, to validate the routine quickly. See 10 Dynamo scripts for Civil 3D that handle tasks like these.
• With a plugin, once the whole office uses it: a button on the Civil 3D top toolbar that runs the full process with your rules.

The guide to automating Civil 3D maps everything you can automate, from points to sheets.