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.
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.
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.
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.
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Illinois Natural Resources Geospatial Data ClearinghouseGenerated by mp version 2.8.25 on Thu Apr 02 09:54:04 2009