Unconsolidated deposits, mainly glacial drift, overlie the bedrock surface in most of Illinois. Glacial drift ranges from less than a few feet to approximately 600 feet in thickness. The thickest drift occurs in major preglacial valleys cut into the bedrock and filled with glacial sediments. Regionally thick drift occurs in the N.E. portions of the state. The thinnest drift, less than 25 feet thick and intersected by numerous bedrock outcrops, occurs widely in southern and western portions of the State. Drift, as shown on this map, may include any of the following: unconsolidated deposits, glacial drift, Wisconsinan deposits, Illinoian deposits, till, glaciofluvial deposits, glaciolacustrine deposit, wind-blown deposits (loess).
In April 2004 edition 2.0 of the data set was transitioned to storage in an Oracle RDBMS using the ArcSDE geodatabase model. The result (this version) is designated Edition 20040423.
Edition 1.0 of this data set was replaced edition 2.0 in June, 1998. The data were reviewed as described in the logical consistency report and process steps for May, 1998. Contour values, which were not included in edition 1.0, were included in version 2.0.
Illinois State Geological Survey, 1994, Glacial Drift in Illinois: Thickness and Character: ISGS GIS Database GISDB_QTGEO.IL_Drift_Thickness, Illinois State Geological Survey, Champaign, Illinois.
This is a Vector data set. It contains the following vector data types (SDTS terminology):
Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000001. Longitudes are given to the nearest 0.000001. Latitude and longitude values are specified in Decimal degrees.
The horizontal datum used is North American Datum of 1983.
The ellipsoid used is Geodetic Reference System 80.
The semi-major axis of the ellipsoid used is 6378137.000000.
The flattening of the ellipsoid used is 1/298.257222.
Polygon Attributes: THICK - thickness of drift 1 - Less than 25 feet 2 - 25 to 50 feet 3 - 50 to 100 feet 4 - 100 to 200 feet 5 - 200 to 300 feet 6 - 300 to 400 feet 7 - 400 to 500 feet 8 - Greater than 500 feet Thick. 9 - No Drift (Driftless Regions)
RANGE - range of thicknesses in feet for that polygon
Arc Attributes: CONTOUR - The contour value for the arc.
These data may be used to determine approximate depth to bedrock in regional areas of the state (eg. townships). The data are not of sufficient detail for use in determining drift thickness for specific locations. The data can be used for physical or environmental models of the state's unconsolidated geologic materials, eg. coupled with geophysical information, satellite imagery, air photos, hydrologic data, or other data in a Geographic Information System at a statewide scale of 1:500,000.
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.
Kemal Piskin & Robert E. Bergstrom, 1975, Glacial Drift In Illinois: Thickness and Character: ISGS Circular 490, Illinois State Geological Survey, Champaign, Illinois.
Kemal Piskin & Robert E. Bergstrom, 1975, Original mylar separate(s) for the map Glacial Drift In Illinois: Thickness and Character: Illinois State Geological Survey, Champaign, Illinois.
Environmental Systems Research , Redlands CA, 1984, Documentation for the Statewide (1:500,000) Data Base Final Report.
Some changes were made, as follows:
Arcs were coded with contour values. This was done with an AML program that assigned contour values to arcs based on the drift thickness values for the adjacent polygons. This processing was done in late 1996, but the updates were not posted to the general-use data set until June of 1998.
The existing set of tics was replaced by the set of tics from the coverage RE-STATE1. These were derived from 7.5 minute quadrangle corners (data set QUAD75) and give a good distribution of tics immediately outside the state boundary.
COVER-ID values were recalculated to be unique.
The features were imported into the ISGS SDE enterprise database following steps outlined in ISGS procedure GISDB_0009.
Person who carried out this activity:
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, Policy on Appropriate Use of Computers and Network Systems at the University of Illinois at Urbana-Champaign.
Attributes were verified against information on the source map by using polygon shading tied to attribute values. Checks were also performed by relating polygon and arc attribute tables and comparing polygon drift thickness range codes with arc drift thickness values. These checks were reiterated by three individuals. There are no known polygon or arc attribute values outside the appropriate domains. There were, however, some anomalous values discovered on the primary source map (Piskin and Bergstrom, 1975, Plate 1) that have been retained in this data set. See logical consistency report.
Horizontal positional accuracy was verified by visual overlay of source and hard-copy plots. Arcs within line-width of source maps were deemed acceptable. For positional accuracy of source maps, see Piskin and Bergstrom (1975), ISGS Circular 490.
See Piskin and Bergstrom (1975), ISGS Circular 490.
Polygon and chain-node topology was present in the source coverage. It was checked for complete chain-node topology (no dangling arcs, except where appropriate), polygon labels (one per polygon, except for universal polygon), boundary values appropriate for map projection and map units, and appropriate "fuzzy" tolerances. The data set meets these parameters. However, there exists at least one instance of anomalous contour labeling on the source map and in this data set. A pair of concentric contours exist in west-central Woodford County which should have a third contour around them labeled 100 feet. The missing contour does not appear on the source mylar for the map. The anomaly could not be reconciled, so it was left as it appeared on the original map. See the small "bulls-eye" contour in west-central Woodford County.
Are there legal restrictions on access or use of the data?
- ISGS information must be obtained directly from the ISGS or from an authorized distributor. Be aware that ISGS information obtained from an unauthorized third party may have been altered subsequent to original distribution, or may no longer be current.
Links to these are provided in the Cross References section.
- ISGS information is the property of and copyrighted by the Board of Trustees of the University of Illinois with all rights reserved. University copyright policy is stated in the General Rules Concerning University Organization and Procedure, Article III, Section 4. A link is provided in the Cross References section.
Individuals or entities may make fair use of copyrighted ISGS material, such as reproducing a single figure or table, or using a brief text quotation, without obtaining formal permission, but in all cases the Illinois State Geological Survey must be credited as the source of the material. To reproduce ISGS information beyond the fair use standard, permission must be obtained from the ISGS Information Office, 615 East Peabody Drive, Champaign, Illinois 61820, 217-333-4747, email@example.com. License fees and a license agreement may be required, depending on the proposed usage.
Map information is to be used at a scientifically and cartographically appropriate scale, that is, at a scale no greater than indicated on the map or as described in the documentation of the map or map data. Map information is not appropriate for, and is not to be used as, a geodetic, legal, or engineering base. Map information has no legal basis in the definition of boundaries or property lines and is not intended as a substitute for surveyed locations such as can be determined by a registered Public Land Surveyor.
The data do not replace the need for detailed site-specific studies.
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The data are intended for use with GIS software. The ISGS uses ESRI ArcGIS software, however, ESRI formats can be imported into many different GIS software packages. It is expected that customers who obtain these data have the technical expertise to use GIS software. The ISGS does not provide software support of any kind.
Illinois Natural Resources Geospatial Data ClearinghouseGenerated by mp version 2.8.25 on Thu Apr 02 09:54:03 2009