The USGS (United States Geological Survey) has been collecting data for mapping for years, and they make that data available to the public. One of those is the National Elevation Dataset. The USGS has Digital Elevation models of a large part of the US available at various scales. While the data is generally too large-scale for serious design purposes, the data can be pretty useful for planning and preliminary work. The challenge can be finding it and then using it in Civil 3D.
But finding the data is easier than ever. The USGS has combined a number of their common data sources into a single location with a map for viewing and downloading: The National Map. The National Map site has a link to download GIS data that takes you directly to the Map download page.
Navigating the Map Download Page
The download page is split into two parts – the left side with the data available and the right side to select the area of interest. Once you select an area and the types of products you desire, a new tab on the left side will open with products, with the available downloads for the area selected.
I’m looking for elevation data, and in the area selected, I only had the 1/3 arc second data available. You can select the Footprint on each data set available to see the area it covers. You also have several formats. I selected the ArcGrid, as it’s pretty easy to load into Civil 3D.
Once you download the file and extract it from its zipped format, there will a series of files, including some shapefiles of the grid area covered. There will also be a folder with the national grid number for the area. The actual ArcGrid file exists in that folder. The particular file that contains the point data you will want to add to the surface is the W001001.adf file (you can see details of the format from the Library of Congress Digital Formats library).
Once we have the grid file, all we have to do is create a surface and use the DEM definition tool to add it to the surface. Civil 3D will process it, and you will get a surface from that data at the end.
Stay tuned for my next blog, which will explore some of the other federal data sets available and how you can use them.