How to get contour lines for a property
Download the USGS 3DEP elevation model for the property from the National Map Downloader (the 1 meter LiDAR DEM where it exists, otherwise the 1/3 arc-second, roughly 10 meter, DEM), reproject it to your State Plane zone in feet, and run a contour tool such as QGIS's Raster > Extraction > Contour. 1 meter LiDAR supports 1 to 2 ft contours in open ground; 10 meter data supports about 5 ft.
Step by step
- Open the USGS National Map Downloader and zoom to the property.
- Under Elevation Products (3DEP), check 1 meter DEM. If nothing comes back, use 1/3 arc-second DEM. Search, then download the GeoTIFF tile that covers the site.
- In QGIS, open the tile and reproject it with Raster > Projections > Warp to your county's State Plane zone (feet). Clip it to the site plus a buffer.
- 3DEP elevations are in meters (NAVD88). For contours in feet, convert first with the Raster Calculator (multiply by 3.28084 for international feet, or 3.280833 for US survey feet).
- Run Raster > Extraction > Contour with the interval you want, then export the lines to DXF or GeoJSON for CAD.
Which interval the data supports
| Source DEM | Typical contour interval |
|---|---|
| 1 m LiDAR (most of the US now) | 1 to 2 ft in open ground |
| 3 m (older LiDAR) | 2 ft |
| 1/3 arc-second, about 10 m | 5 ft or more |
Drawing 1 ft contours from 10 m data produces neat-looking lines that are mostly interpolation. Basesheet raises the interval automatically when the data is coarse and says so on the drawing.
Limits to know
- Collection date. Each LiDAR project has a date, sometimes ten or more years ago. Grading since then won't show.
- Bare earth. The DEM removes buildings and trees. Under dense canopy there are fewer ground returns, so accuracy drops.
- Small features. Curbs, walls, swales narrower than a couple of cells get smoothed away. Water surfaces are flattened.
More on accuracy: LiDAR contours vs a topographic survey.
Everything here is planning-level public data. Confirm boundaries, topography, wetlands and flood status with a licensed surveyor and the right specialists before design decisions depend on them.
Basesheet does all of this for any US address in about 30 seconds, free, with no account.
Build a base planRelated
- How to get real topography into SketchUp
- LiDAR contours vs a topographic survey
- How to make a site base plan from an address
Updated October 2026.