This data set is a digital elevation model (DEM) of Illinois in ArcInfo grid format. The data are stored in UTM coordinates, using a Transverse Mercator projection with the parameters of UTM Zone 16, NAD27. The data have a 30-meter ground resolution. The x- and y-coordinate values are in meters and the z-values are in feet. This DEM is a mosaicked model of USGS 30x30 meter DEMs, showing 1:24,000-SCALE quadrangle map boundaries that extend in an irregular buffer outside the state boundary. The ISGS and USGS shared the cost to update a number of the DEMs from Level 1 (low quality) elevation data to Level 2 (best quality) to make this the highest resolution, statewide DEM coverage currently available. Due to budget constraints, an area in southeastern Illinois area has not been upgraded to Level 2 elevation data. The difference in quality is noticeable by the horizontal striping characteristic of Level 1 elevation data.