This is an Arc/Info coverage showing the general elevation of the top of the Herrin (No. 6) coal in Illinois. These 100-foot isolines were contoured by Earthvision software using more than 22,000 data points. The data was not contoured using fault lines for control and no manual adjustments were made to the contours to reflect the presence of known faults. Limited data were available in the north central and central portions of the state. This data set is intended for use at a scale of 1:750,000.
