THESE DATA HAVE POSITIONAL INACCURACY OF UP TO 600 FEET IN SOME AREAS OF THE STATE. THEY ARE NOT TO BE USED AT SCALES GREATER THAN 1:62,500. THE DATA ARE NOT APPROPRIATE AS A GEODETIC, LEGAL OR ENGINEERING BASE.
The polygon attribute data include meridian, township, range, section and county number (FIPS) designations. The line attributes indicate line type, including the state line, county lines, township and range lines, section lines, Indian treaty boundaries, base lines, principal meridians, and boundaries between areas mapped from different principal meridians.
The nominal scale is 1:62,500. As of 2003, the data are typically distributed in geographic coordinates (longitude and latitude), decimal degrees, and the North American Datum (NAD) of 1983, and this is the default spatial reference of the ArcSDE feature dataset in which the data are stored. The data were originally developed, however, in a custom Lambert Conformal Conic projection and were distributed in that coordinate system for several years.
The data were digitized in the late 1960s, early 1970s, and in 1984-85 from 7.5- and 15-minute USGS topographic quadrangles. Errors in the location of a given feature are dependent on the accuracy of the original maps and on the accuracy of digitizing. Estimates are that features have an average locational error of approximately plus/minus 100 feet. Some areas of the state have a locational error of approximately 600 feet.
In areas of French colonization land grants, where PLSS sections were not actually surveyed, sections and section lines have been added (estimated).
A graphic overview of the township and range system in Illinois is included in the file c451.pdf
The data were originally known as the ILLIMAP System and were created in the late 1960s and early 1970s for the purpose of producing maps of well locations in Illinois for geologic research by the ISGS and others. It was one of the first efforts in the nation to digitally capture public land survey boundaries. The principal originators of the first version were geologists at the ISGS: Dave Swann, Paul DuMontelle, Dick Mast, and Lindell Van Dyke. The data were initially digitized from 7.5- and 15-minute USGS topographic maps, and this work comprises approximately two-thirds of the present data set. The accuracy was stated as follows: "For the townships digitized from 7.5-minute quadrangles, 95.2 percent of the ILLIMAP distances are within 100 feet of the recorded plat distances, and all are within 180 feet. In townships digitized from 15-minute quadrangles, 82.5 percent of the ILLIMAP distances are within 100 feet of the plat distances, and 98.7 percent are within 200 feet." (ISGS Circular 451, p. 13) Subsequent procedures may have affected the locational accuracy of the data. Please refer to the section entitled Horizontal Positional Accuracy Report.
For more information on the origin of the data set, refer to the Process Steps section. Also refer to ISGS Circular 451 (ILLIMAP - A Computer-Based Mapping System for Illinois, Swann, DuMontelle, Mast & Van Dyke, 1970). That publication discusses the original digitizing work, coordinate conversions, methods for the subdivision of regular and irregular sections, and the accuracy of the results. It is included in the standard distribution files under the file name c451.pdf.
The database was maintained by the ISGS Computer Services Unit under Van Dyke's direction until 1985 at which time the data were converted to an ArcInfo coverage. The conversion was accomplished by Environmental Systems Research Institute (ESRI) of Redlands, California, working under contract with the ISGS via the Illinois Department of Energy and Natural Resources and its Lands Unsuitable for Mining Program. The remaining one third of the state was digitized from 7.5-minute quadrangles at this time (1984-85.)
For more information on the original and updated quadrangles used in the digitizing process, including publication dates, please refer to the Cross References section.
Selected small areas have been updated since 1985 as errors were detected. New topographic maps are constantly being published by the USGS. Those data are not routinely incorporated into this data set.
In 2003 the data set was transitioned from the ESRI ArcInfo coverage data model to the ESRI ArcSDE enterprise geodatabase data model. The data are stored in an Oracle relational database management system (RDBMS) and maintained using ArcGIS software.
At present the data are managed by the Geospatial Analysis and Modeling Section of the ISGS.
Recent updates to the data:
In March, 1998 the data set as it stood was designated Edition 1.0 for metadata and version management purposes.
Edition 1.0 of these data was reviewed for internal logical consistency in March, 1998. As a result, several unneeded .AAT and .PAT items were dropped, tics were replaced, two label errors were corrected and a single polygon was removed. COVER-ID values were recalculated to be unique. See logical consistency report and process steps for March, 1998 for more details. The updated coverage was designated Edition 1.1.
Minor corrections to editions 1.1 and 1.2 were made between 1998 and 2002. Refer to the Process Steps section. The most recent updated coverage data set was designated Edition 1.3.
In April, 2003 the data set was transitioned to storage in an Oracle RDBMS using the ArcSDE geodatabase model. New line attributes were added to identify base lines, principal meridians, and the boundaries between areas of the state mapped using different base lines and meridians. At that time this metadata document was significantly updated. The result was designated Edition 2.0.
In 2006 and 2007, seven polygon code errors were detected and corrected. Refer to the Process Steps section. The most recent updated feature class (this one) was designated Edition 2.2.
Any access to these data, Web sites, computer systems, electronic services, and electronic networks is governed by University and campus policies, in particular, but not limited to, the Policy on Appropriate Use of Computers and Network Systems at the University of Illinois at Urbana-Champaign, the ISGS Terms of Use document available at the ISGS Web site, and the University of Illinois Web Privacy Notice.
Links to these are 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, isgs@isgs.illinois.edu. License fees and a license agreement may be required, depending on the proposed usage.
Any use of these data is governed by University and campus policies, in particular, but not limited to, the Policy on Appropriate Use of Computers and Network Systems at the University of Illinois at Urbana-Champaign, the ISGS Terms of Use document available at the ISGS Web site, and the University of Illinois Web Privacy Notice. Links to these are provided in the Cross References section.
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.
For example, section numbers were checked by plotting maps with a unique color for each possible section number (1-36). These check-plots were visually inspected for the proper color-quilt pattern in each township, indicating correct item values. Meridian, county, and township designations were verified in the same way.
There is no quantitative assessment of attribute accuracy available, however, this coverage has been used extensively by ISGS and DNR personnel since 1984, and it can be assumed most attribute errors have been detected and corrected. There are no know arc or polygon attribute values outside the appropriate value domains.
A logical consistency review was performed in March, 1998. At that time the data were maintained in ArcInfo coverage format.
The following checks were made:
The data set was DESCRIBED and coverage files listed to determine the feature types present. In this data set, the following feature types were found and checked: polygons, arcs, labels, and nodes. The presence of spatial indices was also checked.
For PAT and AAT files, each item was checked for the following: domain of allowable values, adherence of values to the domain, definition of attribute items, requirement of all unique values for an item, logic of items redefined over other items, and length of item name as regards conversion to shapefile format.
The topology status of the data set was checked, as were LABELERRORS, NODEERRORS (if appropriate), and the PROJECTION definition.
The presence of a BND file was verified.
The presence and location of TICS were checked.
Polygon and chain-node topology were present. There were no dangling arcs. There was one polygon label per polygon, except for the universe polygon. Boundary values were appropriate for the map projection and map units. The fuzzy tolerance was suitable for the nominal scale of 1:62,500. Several unneeded .AAT and .PAT items were dropped, tics were replaced, two label errors were corrected, and a single polygon was removed. COVER-ID values were recalculated to be unique. See the process steps for March, 1998. There are no known attribute values outside the appropriate domains.
In areas of French colonization land grants, where PLSS sections were not actually surveyed, sections and section lines have been added (estimated) to facilitate the use of the data in the automated determination of locations based on township, range and section values. These areas occur for the most part along the Illinois and Mississippi Rivers. No record remains that would identify the added section lines, short of visual comparison to the topographic maps of any particular area.
In 1995, the state boundary along the Ohio River was officially changed, but these changes have not been incorporated. Also, this coverage does not include the portion of the state boundary that extends into Lake Michigan. Rather, the lake shore is depicted as the state boundary. Some data were digitized from USGS 7.5-minute topographic quadrangles, and some from 15-minute quadrangles. As a result, scale varies within the coverage.
In 1985 the data were converted to an Arc/Info coverage. The conversion was accomplished by Environmental Systems Research Institute (ESRI) of Redlands, California, working under contract with the ISGS via the Illinois Department of Energy and Natural Resources and its Lands Unsuitable for Mining Program. The remaining one third of the present data set was digitized from 7.5-minute quadrangles at this time (1984-85.) Details of the digitizing process are unavailable. It is reasonable to assume the positional accuracy was improved for newly digitized areas. However, it is also likely there was some degradation to the positional accuracy of the previously existing data due to automated coverage processing, for example, the use of the ArcEdit CLEAN command.
Subsequently, the horizontal positional accuracy was spot verified by manual overlay of source and hard-copy plots. Arcs within one line-width of source maps were deemed acceptable. The size of the sample set is unknown. Errors in the location of a given feature are dependent on the accuracy of the original maps and on the accuracy of digitizing and processing. Current estimates are that features in the data set have an average locational error of approximately plus/minus 100 feet. The greatest known locational errors are on the order of 600 feet.
The source maps are subject to USGS mapping accuracy standards. For more information on the source maps used, refer to the Cross References and Process Steps sections.
The data were initially digitized from 7.5- and 15-minute USGS topographic maps, and this work comprises approximately two-thirds of the present data set. A list of these quadrangles is included with the standard distribution file as IL_PLSS_Digitizing_History_Tb.dbf.
For more information on the origin of the data set, see ISGS Circular 451 (ILLIMAP - A Computer-Based Mapping System for Illinois, Swann, DuMontelle, Mast & Van Dyke, 1970). That publication discusses the original digitizing work, coordinate conversions, methods for the subdivision of regular and irregular sections, and the accuracy of the results.
The remaining one third of the state was digitized from 7.5-minute quadrangles at this time (1984-85.) A list of these quadrangles is included in the standard distribution file as IL_PLSS_Digitizing_History_Tb.dbf.
No specifics on the automation process are available. It is assumed the automation process was typical of that for ArcInfo data sets of the time, implying digitization from source maps, editing and error checking with Arc, ArcEdit and ArcPlot, building topology, and subsequent revision and update.
New topographic maps are constantly being published by the USGS. Those data were not routinely incorporated into this data set.
TICS - The data set had eight tics along the northern border of the state. For better tic distribution, these were replaced with ten tics from USGS 30-minute by 60-minute quadrangle corners, evenly distributed around the state. However, users needing registration tics for use with these data (or a subset of these data) should expect to create a task-specific tic set, usually based on section corners.
REMOVAL OF ITEMS - The following empty .AAT items were dropped: STATE2C.OLD#, STATE2C.OLD-ID, ORIG-ID, SYMBOL.
UNIQUE COVER-ID VALUES - COVER-ID values in the .AAT and .PAT were calculated to equal (COVER# - 1) in order to make them unique.
NODEERRORS - These NODEERRORS were corrected:
Polygon 57706 has 2 label points. Label User ID: 58883 Label User ID: 28627 Polygon 57806 has 2 label points. Label User ID: 29333 Label User ID: 29374EXTRA POLYGON - An extra polygon was removed. RE-STATE1# = 57700 in .PAT had TWP = '4 2N 2E'. This polygon should actually be a part of the polygon to the immediate west (RE-STATE1# = 57698, TRS = '4 2N 1E25'). The hardcopy version of the USGS Astoria quad is suspected to be in error - the markings are ambiguous. Meridian, township, range and section designation were verified using 1997 and 1998 plat map books for Mason and Schuyler Counties. The arc that separates the two polygons (re-state# = 123731) was removed. (The ID numbers in this paragraph refer to edition 1.0 of the coverage.)
At this time it was decided to maintain a record of GIS versions of this data set. The data set prior to review was (arbitrarily) designated Edition 1.0. Upon completion of the review, the data set was designated as Edition 1.1.
Was 3, 7N, 13W, 30 Corrected to 3, 7N, 13W, 29
Was 4, 12S, 1W, 6 Corrected to 3, 7N, 13W, 19
(The values are MERIDIAN, TOWNSHIP, RANGE, SECTION)
The updated data set was designated Edition 1.3
The various coverage feature classes were imported using ArcCatalog 8.2.
The label point feature classes for township and section polygons were not imported.
Prior to import, the spatial reference of the data set was changed to Geographic, decimal degrees, NAD83 in double precision. The previous spatial reference was the customary ISGS Lambert Conformal Conic projection.
After import, several informal tests were done to verify that the data were not modified during import.
Also after import, the SDE geodatabase was exported to a personal geodatabase. The IL_PLSS_Section_Ln feature class was edited to add three new fields: BASELINE, MERIDIAN, and MERIDBND. These were edited respectively to identify township, range, and section lines that comprise base lines, principal meridians, and the boundaries between areas mapped from different base lines and meridians. The edited feature classes were successfully re-imported into the SDE geodatabase. This process was performed for three reasons: (1) to add the new attribute data, (2) to test the ability to extract a layer from an SDE feature dataset, edit it, and successfully re-integrate it, and (3) to verify that there was no drift in the XY coordinate values of line vertices in the export and import operation.
Also at this time, this metadata file was considerably rewritten and updated. Of special note are the additional PDF and dBase files that provide a great deal of legacy information about this data set. These are listed in the Cross References section.
Note that upon export from an enterprise SDE database to the coverage format using ArcGIS 8.2, a generic set of tics is created for the coverage. It is assumed they are related in some way to the maximum and minimum extent coordinates for the coverage, however, one of the tics is placed far outside the coverage extent. Therefore, these tics should be ignored.
CALHOUN T08SR02W27 - miscoded 26 - corrected to 27 CALHOUN T08SR02W34 - miscoded 35 - corrected to 34 GREENE T11NR14W24 - miscoded 23 - corrected to 24 PIKE T04SR02W33 - miscoded 34 - corrected to 33 TAZEWELL T23NR07W09 - miscoded 08 - corrected to 09 WOODFORD T27NR04W35 - miscoded 34 - corrected to 35
The updated feature class is designated edition 2.1.
WOODFORD T27NR04W34 - miscoded 33 - corrected to 34
The updated feature class is designated edition 2.2.
Polygon attributes identify the meridian, township, range, section, and county number for sections.
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