Description: Thickness contours of 28", 42", and 66" were mapped for the Colchester (No. 2) Coal in Illinois. This datafile was created from public data only. The term "insufficient data" is used in the delineation of areas where the coal is known to be thin (less than 18 inches thick) or absent, or areas where there is insufficient thickness data for resource calculation and mapping. This map was created as part of the National Coal Resource Assessment being conducted by the USGS. Updates were made to 7 counties as part of a Coal Availability Assessment, 2002.