December 2010 Final Indian Creek, Dago Slough, and Prairie Creek LRS/TMDL
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Common Land Unit (CLU) layer - April 2008
The CLU dataset provides a digitized vector dataset, comprised of farm, tract, and field
boundaries with associated attribute data. FSA defines farm field boundaries as agricultural
land that is delineated by natural and manmade boundaries such as roadways, tree lines,
waterways, fence lines, etc. Using rectified photomaps that have been maintained by FSA
Service Centers as a reference, tract and field boundaries were heads-up digitized, using a
custom designed tool bar. Digitizing was done at a scale of 1:4800 with digital
orthophotography as the base map. Each of the boundaries of the CLU was digitized to a
tolerance of three meters (approximately 10 feet) from ground features visible on the digital
orthophotography. The base orthoimagery used during the CLU digitizing effort was produced
by mosaicing digital orthophoto quarter quads (MDOQs) into a seamless county image.
Data was used to create map(s): CREP and CRP
Illinois State Geological Survey, Champaign, Illinois, USA.
This Arc/Info grid (raster) data set consists of edge-matched USGS 1:250,000 DEM tiles for
Illinois. Cell size is 301 feet and cell values are elevations in meters above mean sea level
rounded to the nearest integer. The data include all of Illinois and extend approximately nine
miles beyond the state boundary. Some elevation data at the edges of individual DEM tiles were
smoothed to remove edge-matching faults. These data were assembled to provide a statewide
database of surface elevation points suitable for analyses of statewide geologic phenomena
associated with elevation. The data have been used to generate slope data and shaded relief
images, and are appropriate for other such regional applications.
Data was used to create map(s): Slope
A 0.5 meter resolution panchromatic (B and W) USGS Digital Orthophoto Quarter-quadrangle
(DOQQ) A DOQQ is a raster image in which displacement in the image caused by sensor
orientation and terrain relief has been removed. DOQQs are produced with a 1-meter ground
sample distance (GSD) and are cast on the Universal Transverse Mercator (UTM) projection on
the North American Datum of 1983 (NAD83). Each DOQQ is produced to meet a National Map
Accuracy Standard (NMAS) for 1:12000 scale maps (10.16 meters radial error at a 90%
probability).NAPP imagery is flown leaf-off in deciduous vegetation regions.
Data was used to create map(s): Location of Homes, Pasture selection for Landuse
FEMA floodzones 1986
This set of 102 tiles depicts by county the 100 year and 500 year floodzones for the
unincorporated areas as indicated on the Federal Emergency Management Agency (FEMA)
National Flood Insurance Program (FIRM) maps and Flood Hazard Boundary maps were
digitized from paper maps. When digitizing, all RMS values were not more than twenty feet.
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