This is a shaded relief image of Illinois in ArcSDE raster 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 source 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 source DEM is stored in the ISGS GIS database as GISDB.IL_DEM_30M_RAS.