Basemappr

Contours to DXF, from USGS 3DEP

Draw a boundary anywhere in the United States, pick a contour interval, and get a georeferenced DXF of elevation contours — usually in under a minute. Exporting takes a sign-in step; your first few can go through it as a guest, with no account and no email.

What USGS 3DEP is

The 3D Elevation Program is the U.S. Geological Survey’s national elevation dataset. Most of the country is covered by airborne lidar flown for 3DEP, published as a seamless bare-earth digital elevation model — ground surface, with vegetation and buildings classified out. It is public-domain data, and it is the same source that sits behind the contours on a USGS topographic map.

Contours here are generated from that DEM on demand, for the boundary you drew, rather than clipped out of a pre-made contour layer. That is what lets you ask for any interval instead of the 2 ft or 10 ft a published layer happens to have been built at.

3DEP is a screening-grade surface, not a survey. It is the right basis for a feasibility pass, a concept grading exercise or an early earthwork estimate; it is not a substitute for a topographic survey when you are sizing walls or setting finished grades.

What the DXF contains

  • Contour polylines at your chosen interval, in feet or metres, one layer named for the product that generated them.
  • Real coordinates, not a drawing parked at the origin — the file is written in the State Plane zone for the area you drew, in US survey feet, unless you ask for a specific EPSG code.
  • An AutoCAD GEODATA section, so the drawing knows where on the earth it is and lines up with anything else georeferenced you bring into the same drawing.

If the elevation service is degraded when your export runs, the job falls back to a coarser ~10 m national DEM rather than failing. When that happens the layer name says so, the contour interval is floored at 5 ft, and the page tells you before you download — fine for a feasibility pass, but re-run it before sizing walls or earthwork.

How it opens in Civil 3D

As a drawing
Open the DXF directly, or INSERT it into an existing drawing. Because it carries its own coordinate system, set your drawing’s zone to the matching State Plane zone and the contours land where they belong against your survey.
As a surface
To build a TIN from the contours, create a surface and add the contour layer under Definition → Contours. Check that your drawing units are feet before you do — the contour elevations are written in the units you asked for, and Civil 3D will not catch the mismatch for you.
In other CAD
The file is ordinary DXF, so BricsCAD, MicroStation, Rhino and QGIS all read it without a translator.

Elevation data courtesy of the U.S. Geological Survey. Need parcels, floodplain, land cover or an output that isn’t DXF? The full workspace has them.