Digital Elevation Models (DEM) are digitized versions of USGS's 7.5 minute topographic maps. With the help of additional software, they may be used to automatically define the base elevations for objects included in air dispersion modeling analyses. These DEM files can be downloaded from this website below. All DEM files on this site are listed based on the letter they begin with and are named based on the USGS quadrangle they represent.

Choose the letter with which the name of the quadrangle begins:

A listing of the IDNR - Air Quality Bureau's current inventory of DEM data is available in Excel spreadsheet format here.