Screen-size image representing the nature of the data. This is a Vector data set. The map projection used is Lambert Conformal Conic. The horizontal datum used is NAD27. The semi-major axis of the ellipsoid used is 6378206.4 meters.
Coverage is intended to identify areas of Illinois where major bedrock aquifers exist.
These data are appropriate for regional thematic analysis. Illinois State Geological Survey, Champaign, Illinois. Illinois State Geological Survey, Champaign, Illinois. Illinois State Geological Survey Circular 232, Illinois State Geological Survey, Champaign, Illinois. Illinois State Geological Survey Bulletin 95, Illinois State Geological Survey, Champaign, Illinois.