More information about this seam.This datafile shows a highly generalized depth to the top of the Danville (No. 7) coal in Illinois. These 100-foot contours were created by Earthvision software using more than 9,500 data from drill holes. Because the depth of the coal was contoured directly from drill hole data (as opposed to creating a map of coal elevation and subtracting it from a map of surface topography) the resulting map is essentially based on the assumption that the land surface is a level plain. Consequently, the accuracy of the map is lowest where the coal is shallowest. Data control was very poor in north-central Illinois and the Eagle Valley area in southeastern Illinois. Because a revised crop of the Danville Coal was not available, this file was originally constructed using the crop of the Herrin Coal. This data set is intended for use at a scale of 1:750,000. This data set was created as part of the ISGS GIS database to show general depth of the Danville (No. 7) Coal seam. The data are appropriate for regional analysis.These data are appropriate for use in local and regional thematic analysis. The data are not appropriate as a geodetic, legal or engineering base. The data set was not and is not intended as a substitute for surveyed locations, such as can be determined by a registered Public Land Surveyor. Although useful in a GIS as a reference base layer for maps, the data set has no legal basis in the definition of boundaries or property lines.

More information about this seam.This datafile shows a highly generalized depth to the top of the Danville (No. 7) coal in Illinois. These 100-foot contours were created by Earthvision software using more than 9,500 data from drill holes. Because the depth of the coal was contoured directly from drill hole data (as opposed to creating a map of coal elevation and subtracting it from a map of surface topography) the resulting map is essentially based on the assumption that the land surface is a level plain. Consequently, the accuracy of the map is lowest where the coal is shallowest. Data control was very poor in north-central Illinois and the Eagle Valley area in southeastern Illinois. Because a revised crop of the Danville Coal was not available, this file was originally constructed using the crop of the Herrin Coal. This data set is intended for use at a scale of 1:750,000. This data set was created as part of the ISGS GIS database to show general depth of the Danville (No. 7) Coal seam. The data are appropriate for regional analysis.These data are appropriate for use in local and regional thematic analysis. The data are not appropriate as a geodetic, legal or engineering base. The data set was not and is not intended as a substitute for surveyed locations, such as can be determined by a registered Public Land Surveyor. Although useful in a GIS as a reference base layer for maps, the data set has no legal basis in the definition of boundaries or property lines.