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•All CDL distribution for the previous crop year
is held until the release of the official NASS county estimates for the major
commodities grown within a given state.
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•Corn and Soybeans are released in March for the
previous crop year – Midwestern States
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•Rice and Cotton are released in June for the
previous crop year – Delta States
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•A freeware browser “ArcReader” from ESRI is
bundled onto the DVD, allowing users without a GIS or image processing
software package to be able to view the CDL products.
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•A demo ArcReader project is on the root
directory of each CDL CD called “PublishedMapDocuments”. The file has a .pmf file extension. Once loaded, the categorized image appears
in the main window, and contains themes from the National Atlas program, also
included are NASS Agricultural Statistical Districts boundaries, and Area
Sampling Frame.
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•For users who have ESRI’s ArcGIS installed on
their Desktop a \MapDocuments folder contains a .mxd project.
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•The shapefiles and images on this DVD are under
no copyright restrictions, as they are considered in the public domain.
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•If you choose to reuse and publish any of the
data this DVD, NASS would appreciate acknowledgment or credit for the usage
of the categorized imagery.
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•NASS publishes all available accuracy
statistics for end-user viewing.
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•The Percent Correct is calculated for each
cover type in the ground truth information, it shows how many of the total
pixels were correctly classified (i.e. across all cover types).
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•“Commission
Error” is the calculated percentage of all pixels categorized to a specific
cover type that were not of that cover type in the ground truth (i.e.
incorrectly categorized).
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•CAUTION: a quoted Percent Correct for a
specific cover type is worthless unless accompanied by its respective
Commission Error.
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•Example: if you classify every pixel in a scene
to “wheat”, then you have a 100% correct wheat classifier (its Commission
Error is also almost 100%).
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•The “Kappa Statistic” is an attempt to adjust
the Percent Correct using information gained from the confusion matrix for
that cover type.
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•Many remote sensing groups use the Percent
Correct and/or Kappa statistics as their final measure of classification
accuracy.
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