This is a statewide polygon feature class of 100 year and 500 year flood zones as of 1986 for the unincorporated areas of Illinois as indicated on Federal Emergency Management Agency (FEMA) National Flood Insurance Program (FIRM) maps and Flood Hazard Boundary maps.
The statewide data layer was created by appending data from 102 county-wide Arc/Info coverages originally released on Illinois DNR GIS data CDs dated 1996.
The data were digitized from paper maps. RMS values were not more than twenty feet in the original digitizing process. Mapscale: 1:6000 to 1:24,000.
Illinois State Water Survey, 1996, One-Hundred and Five-Hundred Year Floodzones for Unincorporated Areas in Illinois: ISGS GIS Database GISDB_HYDRO.IL_Flood_Zones_1986_Py.Online Links:
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.
Coordinates defining the features.
| Value | Definition |
|---|---|
| 0 | not a flood zone |
| 100 | 100-year flood zone |
| 500 | 500-year flood zone |
Sequential unique whole numbers that are automatically generated.
GIS Processing: ISWS and ISGS staff
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, property lines, or flood zones.
APPEND FLOODZONES POLY <list of 98 coverages> END
The coverage was then cleaned, dissolved, and converted to a shapefile:
CLEAN FLOODZONES FLOODZONES2 0.002 0.002 POLY DISSOLVE FLOODZONES2 FLOODZONES3 COLOR POLY (the item COLOR contained the floodzone designations) ARCSHAPE FLOODZONES2 POLY floodzones.shp
The shapefile was imported into a personal geodatabase as a standalone feature class. The polygon data for the remaining four counties (Clark, Franklin, Kankakee, and Lawrence, which had irregular PAT items and definitions) were imported into the feature class using the Load function of ArcCatalog.
The data were then reprojected to lon/lat NAD83 using the Project function of ArcToolbox:
Executing (Project_1): Project C:\floodzones.mdb\floodzone_py C:\floodzones.mdb\floodzone_py_Project GEOGCS['GCS_North_American_1983',DATUM['D_North_American_1983',SPHEROID['GRS_1980',6378137.0,298.257222101]],PRIMEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]] NAD_1927_To_NAD_1983_NADCON Start Time: Thu Aug 17 09:48:45 2006 Executed (Project_1) successfully. End Time: Thu Aug 17 10:11:07 2006 (Elapsed Time: 22 minutes 22 seconds)
The values in field FLOODZONE were changed. Originally 72 indicated 100-year flood zone and 70 indicated 500-year floodzone. These were changed to 100 and 500 respectively.
, University of Illinois Web Privacy Notice.Online Links:
, University Copyright Policy (stated in the General Rules Concerning University Organization and Procedure, Article III, Section 4).Online Links:
, Policy on Appropriate Use of Computers and Network Systems at the University of Illinois at Urbana-Champaign.Online Links:
No report.
No report.
Data are not included for incorporated areas of the state. Data for other areas may also be absent. There has been no quality-control or error checking performed on these data subsequent to compiling the county-by-county coverages into a statewide feature class.
No report.
Are there legal restrictions on access or use of the data?
- Access_Constraints:
- Access to this instance of the data is limited to INRS staff.
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 and the University of Illinois Web Privacy Notice.
Links to these are provided in the Cross References section.
- Use_Constraints:
- These data are not to be distributed outside of the ISGS.
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 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.
217-333-4747 (voice)
isgs@isgs.illinois.edu
Refer to the Legal Notices of Terms and Conditions of the University of Illinois Web Privacy Policy (there is a link in the Cross References section) for policy statements regarding the following:Disclaimer of Liability Disclaimer of Warranties and Accuracy of Data Disclaimer of Endorsement Disclaimer for External Links Disclaimer of Duty to Continue Provision of Data Security Choice of Law
By obtaining these data you agree to the provisions of the University of Illinois Web Privacy Policy, regardless of the manner in which the information was obtained.
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 Clearinghouse
Generated by mp version 2.8.25 on Thu Apr 02 09:54:04 2009