1995. Abert, Curtis C. A digital elevation model (DEM) in ArcINfo grid format. Data were assembled to provide a statewide database of surface elevation points suitable fo... Illinois State Geological Survey.
1995. Abert, Curtis C. Landforms of Illinois with a shaded relief portrayal. Derived from USGS Digital Elevation Model(DEM) data. Illustrates various Illinois landforms i... Illinois State Geological Survey.