USDA, National Agricultural Statistics Service, 2000 Illinois Cropland Data Layer

Metadata:

Identification_Information:
Citation:
Citation_Information:
Originator:
United States Department of Agriculture (USDA), National Agricultural Statistics Service (NASS), Research and Development Division (RDD), Geospatial Information Branch (GIB), Spatial Analysis Research Section (SARS)
Publication_Date: 20010314
Title:
USDA, National Agricultural Statistics Service, 2000 Illinois Cropland Data Layer
Edition: 2000 Edition
Geospatial_Data_Presentation_Form: raster digital data
Publication_Information:
Publication_Place:
USDA, NASS Marketing and Information Services Office, Washington, D.C.
Publisher: USDA, NASS
Other_Citation_Details:
NASS maintains a Frequently Asked Questions (FAQ's) section on the CDL website at <http://www.nass.usda.gov/research/Cropland/SARS1a.htm>. The data is available free for download through CropScape at <http://nassgeodata.gmu.edu/CropScape/>. The data is also available free for download through the Geospatial Data Gateway at <http://datagateway.nrcs.usda.gov/>. See the 'Ordering Instructions' section of this metadata file for detailed Geospatial Data Gateway download instructions.
Online_Linkage: <http://nassgeodata.gmu.edu/CropScape/IL>
Description:
Abstract:
The USDA, NASS Cropland Data Layer (CDL) is a raster, geo-referenced, crop-specific land cover data layer. The 2000 CDL has a ground resolution of 30 meters. The CDL is produced using satellite imagery from the Landsat sensor collected during the current growing season. The Illinois Program represents a cooperative venture between three USDA Agencies (headquarters units of NASS, the Foreign Agriculture Service, and the Farm Service Agency) plus in-state agreements among the Illinois Agricultural Statistics Service, the Illinois Department of Natural Resources and the Illinois Department of Agriculture.
Agricultural training and validation data are derived from the USDA, NASS June Area Survey (JAS). JAS is a national survey based on a stratified random sample of land areas selected from each state's area frame. An area frame is a land use stratification based on percent cultivation. Our enumerators are given questionnaires to ask the farmers what, where, when and how much are they planting. Our surveys focus on cropland, but the enumerators record all land covers within the sampled area of land whether it is cropland or not. NASS uses broad land use categories to define land that is not under cultivation, including; non-agricultural, pasture/rangeland, waste, woods, and farmstead. NASS defines these non-agricultural land use types very broadly, which makes it difficult to precisely know what specific type of land use/cover actually is on the ground. The USDA, NASS recommends that users consider the USGS, National Land Cover Database for studies involving non-agricultural land cover.
Please refer to the 'Supplemental_Information' Section of this metadata file for a complete list of all imagery, ancillary data, and training/validation data used to generate this state's CDL.
The strength and emphasis of the CDL is agricultural land cover. Please note that no farmer reported data are derivable from the Cropland Data Layer.
Purpose:
The purpose of the Cropland Data Layer Program is to use satellite imagery to (1) provide acreage estimates to the Agricultural Statistics Board for the state's major commodities and (2) produce digital, crop-specific, categorized geo-referenced output products.
Supplemental_Information:
If the following table does not display properly, then please visit the following website to view the original metadata file <http://www.nass.usda.gov/research/Cropland/metadata/meta.htm>. 
USDA, National Agricultural Statistics Service 2000 Illinois Cropland Data Layer

CLASSIFICATION INPUTS BY ANALYSIS DISTRICT (AD):
AD01: LANDSAT TM Path 22 Row 32, 03/25 + 08/16/2000
AD02: LANDSAT TM Path 22 Rows 33 & 34, 04/26 + 08/16/2000
AD03: LANDSAT TM Path 23 Row 31, 04/25 + 08/31/2000
AD04: LANDSAT TM Path 23 Row 32, 04/25 + 08/31/2000
AD05: LANDSAT TM Path 23 Rows 33 & 34, 04/25 + 08/31/2000
AD06: LANDSAT TM Path 24 Row 31, 05/02 + 09/07/2000
AD07: LANDSAT TM Path 24 Rows 32 & 33, 05/02 + 09/07/2000

TRAINING AND VALIDATION:
USDA, NASS JUNE AREA SURVEY 2000

NOTE: The final extent of the CDL is clipped to the state boundary
even though the raw input data may encompass a larger area.
Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 20000101
Ending_Date: 20001231
Currentness_Reference: 2000 growing season
Status:
Progress: Complete
Maintenance_and_Update_Frequency: None planned
Spatial_Domain:
Bounding_Coordinates:
West_Bounding_Coordinate: -91.6755
East_Bounding_Coordinate: -87.4834
North_Bounding_Coordinate: 42.4706
South_Bounding_Coordinate: 36.9893
Keywords:
Theme:
Theme_Keyword_Thesaurus: ISO 19115 Topic Category
Theme_Keyword: farming, 001
Theme_Keyword: environment, 007
Theme_Keyword: imageryBaseMapsEarthCover, 010
Theme:
Theme_Keyword_Thesaurus: Global Change Master Directory (GCMD) Science Keywords
Theme_Keyword:
Earth Science > Biosphere > Terrestrial Ecosystems > Agricultural Lands
Theme_Keyword: Earth Science > Land Surface > Land Use/Land Cover > Land Cover

Theme:
Theme_Keyword_Thesaurus: Global Change Master Directory (GCMD) Instrument Keywords
Theme_Keyword: MODIS > Moderate-Resolution Imaging Spectroradiometer

Theme:
Theme_Keyword_Thesaurus: None

Theme_Keyword: crop cover
Theme_Keyword: cropland
Theme_Keyword: agriculture
Theme_Keyword: land cover
Theme_Keyword: crop estimates
Theme_Keyword: AWiFS
Theme_Keyword: MODIS
Theme_Keyword: Landsat
Theme_Keyword: Cropscape
Place:
Place_Keyword_Thesaurus: Global Change Master Directory (GCMD) Location Keywords
Place_Keyword: Continent > North America > United States of America > Illinois
Place:
Place_Keyword_Thesaurus: None
Place_Keyword: Illinois
Place_Keyword: IL

Temporal:
Temporal_Keyword_Thesaurus: None
Temporal_Keyword: 2000
Access_Constraints: None
Use_Constraints:
The USDA, NASS Cropland Data Layer is provided to the public as is and is considered public domain and free to redistribute. The USDA, NASS does not warrant any conclusions drawn from these data. If the user does not have software capable of viewing GEOTIF (.tif) file formats then we suggest using the Cropscape website <http://nassgeodata.gmu.edu/CropScape/> or the freeware browser ESRI ArcGIS Explorer <http://www.esri.com/>.
Point_of_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: USDA, NASS, Spatial Analysis Research Section
Contact_Person: USDA, NASS, Spatial Analysis Research Section staff
Contact_Address:
Address_Type: mailing and physical address
Address: 3251 Old Lee Highway, Room 305
City: Fairfax
State_or_Province: Virginia
Postal_Code: 22030-1504
Country: USA
Contact_Voice_Telephone: 703-877-8000
Contact_Facsimile_Telephone: 703-877-8044
Contact_Electronic_Mail_Address: HQ_RDD_GIB@nass.usda.gov
Data_Set_Credit: USDA, National Agricultural Statistics Service
Security_Information:
Security_Classification_System: None
Security_Classification: Unclassified
Security_Handling_Description: None
Native_Data_Set_Environment:
PEDITOR was used as the main image processing software for the 2000 CDL Program. PEDITOR has been maintained in-house and contains much of the functionality available in commercial image processing systems. However, program/process modifications are relatively easy to support in a research type environment, and the development/release cycle is faster. PEDITOR is deployed in all participating NASS State Statistical Field Offices to handle the ground truthing process and all image processing tasks, and is continuously tested with the Spatial Analysis Research Section (SARS) in Fairfax, Virginia. Currently, PEDITOR runs on most Microsoft Windows platforms; however, PEDITOR's batch processing system programs only runs under Windows NT or 2000.
The hardware requirements for processing this data set are as follows: for digitizing/ground truth editing, any of the 32 bit Microsoft OS's will work. For computationally intensive jobs including; scene processing, clustering, classification, estimation and mosaicking a batch type system is utilized where jobs can be queued on different devices, and the minimum requirements are NT/2000/XP.
Image processing is performed by PEDITOR, where PEDITOR utilizes the Windows console along with environmental variables, and neither are available with 95/98. PEDITOR as it is now constituted, will only run under the Microsoft Windows operating systems.
A Microsoft Visual FoxPro application called the Remote Sensing Project or RSP is used to manage the ground truth collection process, and track each segment to its completion.
Commercial off the shelf software XLNT from Advanced Systems Concepts, allows for batch job processing on the NT/2000/XP operating systems. SARS utilizes XLNT to run computationally intensive jobs that are shared across network resources to expedite processing.
Data_Quality_Information:
Attribute_Accuracy:
Attribute_Accuracy_Report:
If the following table does not display properly, then please visit this internet site <http://www.nass.usda.gov/research/Cropland/metadata/meta.htm> to view the original metadata file. 
***NOTE: The 1997-2010 CDLs were recoded and re-released in January 2012 to better align the historical CDL's with the current
product. Most of these category changes were in the non-agriculture domain. For a detailed list of the category name and code
changes, please visit the Frequently Asked Questions (FAQ's) section at <http://www.nass.usda.gov/research/Cropland/sarsfaqs2>.

USDA, National Agricultural Statistics Service 2000 Illinois Cropland Data Layer

CLASSIFICATION INPUTS BY ANALYSIS DISTRICT (AD):
ANALYSIS DISTRICT AD01
LANDSAT TM / ETM+ PATH: 22, ROWS: 32 - (03/25 & 08/16/2000)
105 CROP / COVER TYPE SIGNATURES, 14 CHANNELS
CDL            CROP /                ORIG. #        ORIG. #        PERCENT        COMMISSION     KAPPA
Code           COVER *               CATEG.         PIXELS         CORRECT *      ERROR          COEFFICIENT
25             ALFALFA               3              6              0              100            -0.01
86             BUILDING              1              450            72.67          3.25           72.42
81             CLOUDS                8              0              0              0              0
1              CORN                  16             20813          97.75          0.08           95.23
62             CROP PAST             2              0              0              0              0
81             FILLER                1              0              0              0              0
62             NON AGG               12             0              0              0              0
44             OTHER CRP             1              0              0              0              0
25             OTHER HAY             0              24             0              0              0
62             OTRWASTE              0              17             0              0              0
62             PERM PAST             2              0              0              0              0
4              SORGHUM               0              22             0              0              0
5              SOYBEANS**            32             16858          99.33          0.43           98.81
51             POPCORN               4              0              0              0              0
59             OTHER CROPS           0              11             0              0              0
82             URBAN                 2              0              0              0              0
83             WATER                 10             0              0              0              0
87             WETLANDS              4              0              0              0              0
24             WIN WHEAT**           5              272            100            41.51          100
63             WOODS                 3              60             83.33          10.71          83.31
               OVERALL                                             97.94                         96.06

ANALYSIS DISTRICT AD02
LANDSAT TM / ETM+ PATH: 22, ROWS: 33 & 34 - (04/26 & 08/16/2000)
165 CROP / COVER TYPE SIGNATURES, 14 CHANNELS
CDL            CROP /                ORIG. #        ORIG. #        PERCENT        COMMISSION     KAPPA
Code           COVER *               CATEG.         PIXELS         CORRECT *      ERROR          COEFFICIENT
25             ALFALFA               0              7              0              0              0
86             BUILDING              0              37             0              0              0
81             CLOUDS                21             0              0              0              0
1              CORN                  5              10280          96.79          0.49           94.97
62             CROP PAST             0              26             0              0              0
81             FILLER                1              0              0              0              0
61             IDLE CROP             4              439            83.6           9.83           83.35
62             NON AGG               7              0              0              0              0
83             OPNWATER              2              72             100            0              100
44             OTHER CRP             2              0              0              0              0
25             OTHER HAY             6              288            94.1           23.01          94.02
62             OTRWASTE              3              248            59.68          41.04          59.31
62             PERM PAST             5              248            87.5           33.02          87.35
4              SORGHUM               0              34             0              0              0
5              SOYBEANS**            38             12362          98.36          3.42           96.99
50             CRP                   0              18             0              0              0
82             URBAN                 4              0              0              0              0
83             WATER                 45             0              0              0              0
87             WETLANDS              4              0              0              0              0
24             WIN WHEAT**           12             617            98.87          59.71          98.8
63             WOODS                 13             2979           94.16          1.99           93.48
               OVERALL                                             95.09                         92.44

ANALYSIS DISTRICT AD03
LANDSAT TM / ETM+ PATH: 23, ROWS: 31 - (04/25 & 08/31/2000)
124 CROP / COVER TYPE SIGNATURES, 14 CHANNELS
CDL            CROP /                ORIG. #        ORIG. #        PERCENT        COMMISSION     KAPPA
Code           COVER *               CATEG.         PIXELS         CORRECT *      ERROR          COEFFICIENT
25             ALFALFA               4              395            85.82          3.42           85.73
86             BUILDING              3              589            32.6           14.67          32.3
1              CORN                  23             25469          98.64          0.86           97.34
81             FILLER                1              0              0              0              0
88             GRASS                 4              56             96.43          73.27          96.41
61             IDLE CROP             0              15             0              0              0
62             NON AGG               3              10             0              100            -0.64
83             OPNWATER              0              23             0              0              0
25             OTHER HAY             0              5              0              0              0
62             OTRWASTE              6              230            62.17          44.57          61.98
62             PERM PAST             2              84             96.43          25             96.42
84             ROADSRR               0              8              0              0              0
5              SOYBEANS              15             21345          98.68          1.67           97.76
57             SWEET CORN FRESH      0              4              0              0              0
59             OTHER CROPS           5              601            84.03          6.13           83.86
82             URBAN                 18             0              0              0              0
83             WATER                 20             0              0              0              0
87             WETLANDS              8              1122           97.5           1.26           97.45
24             WIN WHEAT             4              458            100            0              100
63             WOODS                 8              1493           91.96          4.25           91.73
               OVERALL                                             97.14                         95.15

ANALYSIS DISTRICT AD04
LANDSAT TM / ETM+ PATH: 23, ROWS: 32 - (04/25 & 08/31/2000)
107 CROP / COVER TYPE SIGNATURES, 14 CHANNELS
CDL            CROP /                ORIG. #        ORIG. #        PERCENT        COMMISSION     KAPPA
Code           COVER *               CATEG.         PIXELS         CORRECT *      ERROR          COEFFICIENT
25             ALFALFA               4              225            98.22          10.53          98.22
86             BUILDING              0              719            0              0              0
1              CORN                  17             69555          97.15          1.09           94.17
81             FILLER                1              0              0              0              0
61             IDLE CROP             0              42             0              0              0
62             NON AGG               1              0              0              0              0
25             OATS                  0              32             0              0              0
44             OTHER CRP             1              0              0              0              0
25             OTHER HAY             0              41             0              0              0
62             OTRWASTE              10             538            64.13          68.66          63.83
62             PERM PAST             5              337            93.18          26.81          93.15
4              SORGHUM               0              21             0              0              0
5              SOYBEANS**            18             60229          98.62          3.09           97.44
52             SNAP BEANS            0              44             0              0              0
54             PUMPKINS              3              322            100            0.31           100
58             SWEET CORN PROC       4              422            98.1           0              98.1
59             OTHER CROPS           0              7              0              0              0
82             URBAN                 2              0              0              0              0
83             WATER                 20             0              0              0              0
87             WETLANDS              8              177            24.29          17.31          24.26
24             WIN WHEAT**           3              304            100            0              100
63             WOODS                 11             731            91.93          37.37          91.86
               OVERALL                                             96.78                         93.9

ANALYSIS DISTRICT AD05
LANDSAT TM / ETM+ PATH: 23, ROW(S): 33 & 34 - (04/25 & 08/31/2000)
203 CROP / COVER TYPE SIGNATURES, 14 CHANNELS
CDL            CROP /                ORIG. #        ORIG. #        PERCENT        COMMISSION     KAPPA
Code           COVER *               CATEG.         PIXELS         CORRECT *      ERROR          COEFFICIENT
25             ALFALFA               3              179            97.77          9.33           97.76
86             BUILDING              1              701            5.85           38.81          5.74
81             CLOUDS                6              0              0              0              0
1              CORN                  15             20398          97.6           4.6            96.22
62             CROP PAST             2              56             98.21          45.54          98.21
81             FILLER                1              0              0              0              0
88             GRASS                 0              3              0              0              0
61             IDLE CROP             12             1852           71.76          14.48          70.97
62             NON AGG               0              1              0              0              0
25             OATS                  0              1              0              0              0
83             OPNWATER              1              236            91.53          0              91.49
44             OTHER                 1              0              0              0              0
25             OTHER HAY             7              454            93.61          32.54          93.54
62             OTRWASTE              14             951            34.7           74.2           33.21
62             PERM PAST             8              976            63.01          10.35          62.56
84             ROADSRR               0              4              0              0              0
4              SORGHUM               4              548            73.36          2.19           73.17
5              SOYBEANS**            33             21978          95.61          5.22           92.84
50             CRP                   3              210            90.95          30.29          90.91
59             OTHER CROPS           0              5              0              0              0
82             URBAN                 7              0              0              0              0
83             WATER                 45             0              0              0              0
87             WETLANDS              4              1398           47.28          6.64           46.62
24             WIN WHEAT**           27             2434           97.53          54.57          97.29
63             WOODS                 23             4888           93.72          15.65          93.06
               OVERALL                                             89.85                         85.71

ANALYSIS DISTRICT AD06
LANDSAT TM / ETM+ PATH: 24, ROWS: 31 - (05/02 & 09/07/2000)
140 CROP / COVER TYPE SIGNATURES, 14 CHANNELS
CDL            CROP /                ORIG. #        ORIG. #        PERCENT        COMMISSION     KAPPA
Code           COVER *               CATEG.         PIXELS         CORRECT *      ERROR          COEFFICIENT
25             ALFALFA               3              287            99.3           0.7            99.3
86             BUILDING              0              56             0              0              0
81             CLOUDS                29             0              0              0              0
1              CORN                  38             23156          98.51          1.69           96.48
62             CROP PAST             0              4              0              0              0
81             FILLER                1              0              0              0              0
88             GRASS                 0              17             0              0              0
61             IDLE CROP             0              37             0              0              0
62             NON AGG               1              10             0              100            -0.37
44             OTHER                 1              0              0              0              0
44             OTHER CRP             2              0              0              0              0
25             OTHER HAY             0              10             0              0              0
62             OTRWASTE              7              63             96.83          48.74          96.82
62             PERM PAST             3              484            77.69          2.08           77.47
5              SOYBEANS              12             15313          95.85          2.01           93.39
53             STATE563              3              121            99.17          0              99.17
57             SWEET CORN FRESH      0              3              0              0              0
52             URBAN                 2              0              0              0              0
83             WATER                 22             0              0              0              0
87             WETLANDS              3              0              0              0              0
24             WIN WHEAT             0              11             0              0              0
63             WOODS                 13             653            99.23          8.47           99.22
               OVERALL                                             96.9                          94.11

ANALYSIS DISTRICT AD07
LANDSAT TM / ETM+ PATH: 24, ROWS: 32 & 33 - (05/02 & 09/07/2000)
166 CROP / COVER TYPE SIGNATURES, 14 CHANNELS
CDL            CROP /                ORIG. #        ORIG. #        PERCENT        COMMISSION     KAPPA
Code           COVER *               CATEG.         PIXELS         CORRECT *      ERROR          COEFFICIENT
25             ALFALFA               2              70             92.86          9.72           92.85
86             BUILDING              0              447            0              0              0
81             CLOUDS                31             0              0              0              0
1              CORN                  16             30130          97.76          0.52           95.74
62             CROP PAST             1              77             100            6.1            100
81             FILLER                1              0              0              0              0
88             GRASS                 1              111            99.1           5.17           99.1
61             IDLE CROP             6              779            83.44          11.8           83.24
62             NON AGG               2              0              0              0              0
25             OATS                  0              3              0              0              0
83             OPNWATER              1              101            99.01          0              99.01
44             OTHER CRP             1              0              0              0              0
25             OTHER HAY             1              50             62             8.82           61.98
62             OTRWASTE              9              1378           11.61          81.86          10.34
62             PERM PAST             7              617            93.68          27.02          93.6
84             ROADSRR               0              30             0              0              0
5              SOYBEANS**            14             24542          98.78          1.14           97.99
50             CRP                   0              2              0              0              0
52             SNAP BEANS            0              38             0              0              0
54             PUMPKINS              2              222            92.79          0              92.77
58             SWEET CORN PROC       4              404            100            0              100
59             OTHER CROPS           0              30             0              0              0
82             URBAN                 4              0              0              0              0
83             WATER                 34             0              0              0              0
87             WETLANDS              10             2              100            0              100
24             WIN WHEAT**           4              244            92.62          58.98          92.56
63             WOODS                 16             3160           90.44          29.01          89.78
               OVERALL                                             94.76                         91.45
Quantitative_Attribute_Accuracy_Assessment:
Attribute_Accuracy_Value:
Classification accuracy is generally 85% to 95% correct for the major crop-specific land cover categories. See the 'Attribute Accuracy Report' section of this metadata file for the detailed accuracy report.
Attribute_Accuracy_Explanation:
The strength and emphasis of the CDL is crop-specific land cover categories. NASS collects the remote sensing Acreage Estimation Program's field level training data during the June Agricultural Survey. This is a national survey based on a stratified random sample of land areas selected from each state's area frame. An area frame is a land use stratification based on percent cultivation. Our enumerators are given questionnaires to ask the farmers what, where, when and how much are they planting. Our surveys focus on cropland, but the enumerators record all land covers within the sampled area of land whether it is cropland or not. NASS uses broad land use categories to define land that is not under cultivation, including; non-agricultural, pasture/rangeland, waste, woods, and farmstead. NASS defines these non-agricultural land use types very broadly, which makes it difficult to precisely know what specific type of land use/cover actually is on the ground. The USDA, NASS recommends that users consider the USGS, National Land Cover Database for studies involving non-agricultural land cover.
These definitions of accuracy statistics were derived from the following book: Congalton, Russell G. and Kass Green. Assessing the Accuracy of Remotely Sensed Data: Principles and Practices. Boca Raton, Florida: CRC Press, Inc. 1999. The 'Producer's Accuracy' is calculated for each cover type in the ground truth and indicates the probability that a ground truth pixel will be correctly mapped (across all cover types) and measures 'errors of omission'. An 'Omission Error' occurs when a pixel is excluded from the category to which it belongs in the validation dataset. The 'User's Accuracy' indicates the probability that a pixel from the CDL classification actually matches the ground truth data and measures 'errors of commission'. The 'Commission Error' represent when a pixel is included in an incorrect category according to the validation data. It is important to take into consideration errors of omission and commission. For example, if you classify every pixel in a scene to 'wheat', then you have 100% Producer's Accuracy for the wheat category and 0% Omission Error. However, you would also have a very high error of commission as all other crop types would be included in the incorrect category. The 'Kappa' is a measure of agreement based on the difference between the actual agreement in the error matrix (i.e., the agreement between the remotely sensed classification and the reference data as indicated by the major diagonal) and the chance agreement which is indicated by the row and column totals. The 'Conditional Kappa Coefficient' is the agreement for an individual category within the entire error matrix.
Logical_Consistency_Report:
The accuracy of the land cover classifications are evaluated using the extensive training data collected in the annual NASS June Agricultural Survey (JAS).
Completeness_Report: The entire state is covered by the Cropland Data Layer.
Positional_Accuracy:
Horizontal_Positional_Accuracy:
Horizontal_Positional_Accuracy_Report:
The categorized images are co-registered to EarthSat Inc's ortho-rectified GeoCover Stock Mosaic images using automated block correlation techniques. The block correlation is run against band two of each original raw satellite image and band two of the GeoCover Stock Mosaic. The resulting correlations are applied to each categorized image, and then added to a master image or mosaic using PEDITOR. The EarthSat images were chosen as they provide the best available large area ortho-rectified images as a basis to register large volume Landsat images with.
Quantitative_Horizontal_Positional_Accuracy_Assessment:
Horizontal_Positional_Accuracy_Value: 50 meters root mean squared error overall
Horizontal_Positional_Accuracy_Explanation:
The GeoCover Stock Mosaics are within 50 meters root mean squared error overall. The publisher of the GeoCover mosaic is MDA Federal (previously Earthsat).
Lineage:
Source_Information:
Source_Citation:
Citation_Information:
Originator:
United States Geological Survey (USGS), Earth Resources Observation and Science (EROS)
Title:
Landsat 5 Thematic Mapper (TM) and Landsat 7 Enhanced Thematic Mapper Plus (ETM+)
Geospatial_Data_Presentation_Form: remote-sensing image
Publication_Information:
Publication_Place: Sioux Falls, South Dakota, USA
Publisher: USGS EROS Data Center
Publication_Date: 2000 growing season
Other_Citation_Details:
The Landsat 5 TM and Landsat 7 ETM+ data is free for download through the following website <http://glovis.usgs.gov/>. Additional information about Landsat data can be obtained at <http://eros.usgs.gov/>. Refer to the 'Supplemental Information' Section of this metadata file for specific scene date, path and rows used as classification inputs.
Source_Scale_Denominator: 30 meter
Type_of_Source_Media: CD-ROM and/or DVD; online download
Source_Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 20000101
Ending_Date: 20001231
Source_Currentness_Reference: ground condition
Source_Contribution: Raw data used in land cover spectral signature analysis
Source_Information:
Source_Citation:
Citation_Information:
Originator: National Aerial Photography Program (NAPP)
Publication_Date: variable
Title: NAPP aerial photographs
Geospatial_Data_Presentation_Form: remote-sensing image
Publication_Information:
Publication_Place: Salt Lake City, Utah, USA
Publisher: Aerial Photography Field Office (AFPO)
Other_Citation_Details:
Additional information about NAPP:EROS Data CenterSioux Falls, South Dakota 57198, USA Phone (605)594-6151 fax x6589
Source_Scale_Denominator: 8000
Type_of_Source_Media: paper
Source_Time_Period_of_Content:
Time_Period_Information:
Single_Date/Time:
Calendar_Date: variable
Source_Currentness_Reference: ground condition
Source_Contribution: spatial and attribute information
Source_Information:
Source_Citation:
Citation_Information:
Originator:
USDA/NASS, Research and Development Division, Area Frame Section
Publication_Date: 1975
Title: Area Sampling Frame (ASF) of Illinois
Geospatial_Data_Presentation_Form: vector digital data
Publication_Information:
Publication_Place: Washington D.C., USA
Publisher: USDA-NASS
Other_Citation_Details:
Additional information about the NASS Area Frame Stratification can be obtained from the following internet site: <http://www.nass.usda.gov/research/stratafront2b.htm>
Source_Scale_Denominator: 100000
Type_of_Source_Media: online
Source_Time_Period_of_Content:
Time_Period_Information:
Single_Date/Time:
Calendar_Date: 1975
Source_Currentness_Reference: publication date
Source_Contribution: spatial and attribute information
Process_Step:
Process_Description:
The Cropland Data Layer (CDL) Program provides the National Agricultural Statistics Service (NASS) with internal proprietary county and state level acreage indications of major crop commodities, and secondarily provides the public with "statewide" (where available) raster, geo-referenced, categorized land cover data products after the public release of county estimates. This project builds upon the USDA's National Agricultural Statistics Service (NASS) traditional crop acreage estimation program, and integrates the enumerator collected ground survey data with satellite imagery to create an unbiased statistical estimator of crop area at the state and county level for internal use. No farmer reported data is revealed, nor can it be derived in the publicly releasable Cropland Data Layer product.
Every June thousands of farms are visited by enumerators as part of the USDA/NASS June Agricultural Survey (JAS). These farmers are asked to report the acreage, by crop, that has been planted or that they intend to plant, and the acreage they expect to harvest. Approximately 11,000 area segments are selected nationwide for the JAS. The segment size can range in size from about 1 square mile in cultivated areas to 0.1 of a square mile in urban areas, to 2-4 square miles for larger probability proportional to size (PPS) segments in rangeland areas. This division allows intensively cultivated land segments to be selected with a greater frequency than those in less intensively cultivated areas. The 150-400 square miles of ground truth collected during the JAS provides a great ground truth training set annually.
The Area Sampling Frame (ASF) is a stratification of each state into broad land use categories according to the percentage of cropland present. The ASF is stratified using visual interpretation of satellite imagery. The sampling frames are constructed by defining blocks of land whose boundaries are physical features on the ground (roads, railroads, rivers, etc). These blocks of land cover the entire state, do not overlap, and are placed in strata based on the percent of land in the block that is cultivated. The strata allow for efficient sampling of the land, as an agriculturally intensive area will be more heavily sampled than a non ag intensive area.
The enumerators draw off field boundaries onto NAPP 1:8,000 black and white aerial photos containing the segment, according to their observations and the farmer reported information. The fields are labeled and the cover type is recorded using a grease pencil on the aerial photo. Enumerators account for every field/land use type within a segment. They assign each field a cover type based upon a fixed set of land use classes for each state. Every field within a segment must fit into one of the pre-defined classes.
The program methodology is a continuous process throughout the year. The first step "Segment Preparation" establishes the training segments, digitizes the perimeters, and distributes software and data to the field offices, this goes from February to late May. Segment digitizing begins during the JAS and continues until all fields and all segments are completely digitized, this may run thru July or even until mid-October in some states depending on human resource availability. Segment cleanup analyzes the newly digitized segments with the new acquired imagery. Fields that are bad either by digitizing or cover type are corrected or removed from training. Scene processing fits each segment onto a scene by shifting, and cloud-influenced segments are removed. The cluster/classification process runs in concert with the scene processing steps, as segments are shifted they can be clustered. This process is iterative, and can run into December. Estimation can be performed once a scene is finished classification, and the user is satisfied with the outputs. Estimation can begin as early as late October and run into late January/February. The mosaic process runs once estimation is completed. It is also iterative and can go from late December to March. The mosaic for a particular state is released once the county estimates are officially released for that state.
Scene selection begins in early summer, and could run into the late fall depending on image availability. The Cropland Data Layer program primarily uses the Landsat platform for acreage estimation. However, other platforms such as Spot and the Indian IRS platforms are used to fill "data acquisition" holes within a state. A spring and summer date of observation is preferred for maximum crop cover separation for multi-temporal analysis of summer crops. If only one date of observation is available (unitemporal), a mid summer date is preferred. If only an early spring date March-May or a fall date September-October is available (unitemporal) during the growing season, then it is best to not use that scene or analysis district for estimation, as bare soil in the spring and fully senesced crops in the fall will provide erroneous results.
The clustering/classification is an iterative process, as fields get misclassified, they can be fixed or marked as bad for training and reprocessed. Known pixels are separated by cover type and clustered, within cover type using a modified ISODATA clustering algorithm, as it allows for merging and splitting of clusters. Modified implies that the output clusters are not labeled (other than as coming from the input cover type) as they can be reassigned later if desired. Clustering is done separately for each cover type (or specified combination of cover types, such as all small grains). The clustered cover types are then assembled together into one signature file, where entire scenes are classified using the maximum likelihood algorithm. Clustering is based on the LARSYS (Purdue University) ISODATA algorithm. It performs an iterative process to divide pixels into groups based on minimum variance. The pairs of clusters in close proximity (based on Swain-Fu distance) are merged. High variance clusters can be split into two clusters (variance of first principal component is used as a measure). The output of any clustering program is a statistics file which stores mean vectors and covariance matrices of final set of clusters.
The outputs are a categorized or classified image in PEDITOR format and the associated accuracy statistics for each cover type. The maximum likelihood classifier performs a pixel-by-pixel classification based on the final, combined statistics file. It calculates the probability of each pixel being from each signature; then classifies a pixel to the category with highest probability. The processing time depends on size of file to be classified (i.e. number of pixels), number of categories in the statistics file and number of input dimensions (number of bands/pixel).
For estimation purposes, clouds can be minimized by defining Analysis Districts (AD) along adjacent scene edges, by cutting the Analysis Districts by county boundary, or cutting the clouds out by primary sampling units. Analysis Districts can be individual or multiple scenes footprints that have to be observed on the same date, and analyzed as one. An AD can be comprised of one or more scenes. An AD can be defined by either a scene edge or a county boundary. Multi-temporal AD's are possible as long as both dates in all scenes are the same. A single or multi-scene AD will use all potential training fields for clustering/classification/estimation. Several factors can lead to problems in a classification, some get corrected in early edits and some do not:
Several factors can lead to problems in a classification, some get corrected in early edits and some do not: poor imagery dates, with respect to the major crops of interest, complete training fields that are incorrectly identified in the ground truth, parts of training fields that are not the same as the major crop or cover type, irrigation ditches, wooded areas, low spots filled with water, and/or bare soil areas in an otherwise vegetated field. Crops that look alike to the clustering algorithm(s) due to planting/growing cycle: spring wheat and barley at almost any time, crops in senescence, and grassy waste fields and idle cropland. Cover types that are essentially the same but used differently: wooded pasture versus woods or waste fields (only difference may be the presence of livestock), corn for grain versus corn silage, and cover crops such as rye and oats. Cover types that change signatures back and forth during the growing season: alfalfa and other hays before and after cutting, with multiple cuttings per year. Once the analyst is satisfied with the classification, the next step can be acreage estimation or image mosaicking.
Three estimation methods are available for each AD: regression, pixel ratio and direct expansion. Where available, regression is chosen as the preferred type of estimation. This approach essentially corrects the area sample (ground only) estimate based on the relationship found between reported data and classified pixels in each stratum where it is used. A regression relationship should be based on 10 or more segments for any stratum used. Where there are not enough segments in each stratum, a pixel based ratio estimator may be used which essentially combines data across stratum to get the relationship. Finally, the direct expansion (total number of possible segments times the average for sampled segment) may be used in the absence of pixel based methods. Regression adjusts the direct expansion estimate based on pixel information. It usually leads to an estimate with a much lower variance than direct expansion alone. Segments, called outliers, which do not fit the linear relationship estimated by the regression are reviewed; if errors are found, they are corrected or that segment may be removed from consideration in the analysis.
Full scene classifications (large scale) are run wherever the regression or pixel ratio estimates are usable. Estimates derived from the classification are compared to the ground data to make one final check. State estimates are made by summing pixel based estimators where available and ground data only estimators everywhere else. County estimates are then derived from the state estimates using a similar approach. Final numbers are delivered to state field offices and the NASS Agricultural Statistics Board for their use in setting the official final estimates. The states also have administrative data, such as FSA certified acres at the county level, and other NASS survey data. Every 5th year, NASS also performs the Census of Agriculture at the county level.
The Landsat TM/ETM+ scenes that SARS uses are radiometrically and systematically corrected. There is a need to tie down registration points on a continuing basis for every state in the project. Without some image/image registration, the scene registration tends to float 2-3 pixels in any given direction, for any given scene. Manual registration for every scene of every project, would be nearly impossible, as the CDL is on a repeating production cycle every year, and human resource levels for this process are low. Image recoding is necessary between different analysis districts, to rectify to a common signatures set for a state. Clouds pose a problem when trying to make acreage estimates, and there are mechanisms within Peditor to minimize their extent, as there are ways to minimize cloud coverage in the mosaic process by prioritizing scene overlap.
Each categorized scene is co-registered to EarthSat's GeoCover LC imagery (50 meters RMS), and then stitched together using Peditor's Batch program. A block correlation is run between band two from each raw scene, and band two of the ortho-base image. The registration of the GeoCover mosaicked scene and the individual raw input scenes are used to get an approximate correspondence. A correlation procedure is used on the raw Landsat scenes and the mosaicked scene to get an exact mapping of each pixel from the input Landsat scenes to the mosaicked scene. The results of the correlation are used to remap the pixels from the individual input scenes into the coordinate system of the mosaicked scene. The mosaic process now performs: 1) Precision registration of images automatically, 2) Converts each categorized image and associated statistics file to a set standard automatically (recode), 3) Specify overlap priority by scene or county, 4) Filters out clouds when possible. The scenes are stitched together using the priorities previously assigned from the scene observation dates/analysis districts map. Scenes/analysis districts with better quality observation dates are assigned a higher priority when stitching the images together. Clouds are assigned a null value on all scenes, and scenes of lower priority that are cloud free, take precedence over clouded higher priority images. Once cloud cover is established throughout the mosaic the clouds are assigned a digital value.
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. Corn and Soybeans are released in March for the previous crop year - Midwestern States. Rice and Cotton are released in June for the previous crop year - Delta States. Small grains are released in March for the Great Plains States.
NASS publishes all available accuracy statistics for end-user viewing. The Percent Correct is calculated for each cover type in the ground truth, it shows how many of the total pixels were correctly classified (i.e. across all cover types). '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). CAUTION: a quoted Percent Correct for a specific cover type is worthless unless accompanied by its respective Commission Error. Example: if you classify every pixel in a scene to 'wheat', then you have a 100% correct wheat classifier (however its Commission Error is also almost 100%). The 'Kappa Statistic' is an attempt to adjust the Percent Correct using information gained from the confusion matrix for that cover type. Many remote sensing groups use the Percent Correct and/or Kappa statistics as their final measure of classification accuracy.
PUBLIC RELEASE: The USDA, NASS Cropland Data Layer is considered public domain and free to redistribute. The official website is <http://www.nass.usda.gov/research/Cropland/SARS1a.htm>. The data is available free for download through CropScape <http://nassgeodata.gmu.edu/CropScape/> and the Geospatial Data Gateway <http://datagateway.nrcs.usda.gov/>. See the 'Ordering Instructions' section of this metadata file for detailed download instructions. Please note that in no case are farmer reported data revealed or derivable from the public use Cropland Data Layer.
Process_Date: 2000
Process_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: USDA, NASS, Spatial Analysis Research Section
Contact_Person: USDA, NASS, Spatial Analysis Research Section staff
Contact_Address:
Address_Type: mailing and physical address
Address: 3251 Old Lee Highway, Room 305
City: Fairfax
State_or_Province: Virginia
Postal_Code: 22030-1504
Country: USA
Contact_Voice_Telephone: 703-877-8000
Contact_Facsimile_Telephone: 703-877-8044
Contact_Electronic_Mail_Address: HQ_RDD_GIB@nass.usda.gov
Cloud_Cover:
Generally, there is enough cloud-free satellite imagery available during the growing season that there will be no cloud cover in the published CDL. Older versions of the CDL (2005 and earlier) may contain significant cloud cover due to available imagery and processing limitations, which have since been overcome. Reference the attribute information within the specific CDL state and year image file to verify the extent of cloud cover.
Spatial_Data_Organization_Information:
Indirect_Spatial_Reference: Illinois
Direct_Spatial_Reference_Method: Raster
Raster_Object_Information:
Raster_Object_Type: Pixel
Row_Count: 20629

Column_Count: 11380

Spatial_Reference_Information:
Horizontal_Coordinate_System_Definition:
Planar:
Grid_Coordinate_System:
Grid_Coordinate_System_Name:
FOR GEOSPATIAL DATA GATEWAY USERS: Universal Transverse Mercator (UTM) Due to technical restrictions, the online data available free for download through the Geospatial Data Gateway <http://datagateway.nrcs.usda.gov/> can only be offered in UTM. However, the official Cropland Data Layer available at <http://nassgeodata.gmu.edu/CropScape/> includes the data in its native Albers Conical Equal Area coordinate system.

FOR CROPSCAPE USERS: Albers Conical Equal Area is the native projection used in the production of the Cropland Data Layer. The projection parameters for the Albers projection are as follows: 
Map_Projection_Name: Albers Conical Equal Area
Albers_Conical_Equal_Area:
Standard_Parallel: 29.500000
Standard_Parallel: 45.500000
Longitude_of_Central_Meridian: -96.000000
Latitude_of_Projection_Origin: 23.000000
False_Easting: 0.000000
False_Northing: 0.000000
Planar_Coordinate_Information:
Planar_Coordinate_Encoding_Method: row and column
Coordinate_Representation:
Abscissa_Resolution: 30
Ordinate_Resolution: 30
Planar_Distance_Units: meters
Geodetic_Model:
Horizontal_Datum_Name: North American Datum of 1983
Ellipsoid_Name: Geodetic Reference System 80
Semi-major_Axis: 6378137.000000
Denominator_of_Flattening_Ratio: 298.257223563
Universal_Transverse_Mercator:
UTM_Zone_Number: 16 North
Transverse_Mercator:
Scale_Factor_at_Central_Meridian: 0.9996
Longitude_of_Central_Meridian: -87
Latitude_of_Projection_Origin: 0
False_Easting: 500000
False_Northing: 0
Planar_Coordinate_Information:
Planar_Coordinate_Encoding_Method: coordinate pair
Coordinate_Representation:
Abscissa_Resolution: 30
Ordinate_Resolution: 30
Planar_Distance_Units: meters
Geodetic_Model:
Horizontal_Datum_Name: WGS84
Ellipsoid_Name: WGS84
Semi-major_Axis: 6378137.00

Denominator_of_Flattening_Ratio: 298.257223563
Entity_and_Attribute_Information:
Overview_Description:
Entity_and_Attribute_Overview:
NASS collects the remote sensing Acreage Estimation Program's field level training data during the June Agricultural Survey. This is a national survey based on a stratified random sample of land areas selected from each state's area frame. An area frame is a land use stratification based on percent cultivation. The selected areas are targeted toward cultivated parts of each state based on its area frame. Our enumerators are given questionnaires to ask the farmers what, where, when and how much are they planting. Our surveys focus on cropland, but the enumerators record all land covers within the sampled area of land whether it is cropland or not. NASS uses broad land use categories to define land that is not under cultivation, including; non-agricultural, pasture/rangeland, waste, woods, and farmstead. NASS defines these non-agricultural land use types very broadly, which makes it difficult to precisely know what specific type of land use/cover actually is on the ground. Thus, the USDA, NASS recommends that users consider the USGS, National Land Cover Database (NLCD) for studies involving non-agricultural land cover.
Entity_and_Attribute_Detail_Citation:
If the following table does not display properly, then please visit the following website to view the original metadata file <http://www.nass.usda.gov/research/Cropland/metadata/meta.htm>. 
 Data Dictionary: USDA, National Agricultural Statistics Service, 2000 Cropland Data Layer

 Source: USDA, National Agricultural Statistics Service

 The following is a cross reference list of the categorization codes and land covers.
 Note that not all land cover categories listed below will appear in an individual state.

 Raster
 Attribute Domain Values and Definitions: NO DATA, BACKGROUND 0

 Categorization Code   Land Cover
           "0"       Background

 Raster
 Attribute Domain Values and Definitions: CROPS 1-20

 Categorization Code   Land Cover
           "1"       Corn
           "2"       Cotton
           "3"       Rice
           "4"       Sorghum
           "5"       Soybeans
           "6"       Sunflower
          "10"       Peanuts
          "11"       Tobacco
          "12"       Sweet Corn
          "13"       Pop or Orn Corn
          "14"       Mint

 Raster
 Attribute Domain Values and Definitions: GRAINS,HAY,SEEDS 21-40

 Categorization Code   Land Cover
          "21"       Barley
          "22"       Durum Wheat
          "23"       Spring Wheat
          "24"       Winter Wheat
          "25"       Other Small Grains
          "26"       Dbl Crop WinWht/Soybeans
          "27"       Rye
          "28"       Oats
          "29"       Millet
          "30"       Speltz
          "31"       Canola
          "32"       Flaxseed
          "33"       Safflower
          "34"       Rape Seed
          "35"       Mustard
          "36"       Alfalfa
          "37"       Other Hay/Non Alfalfa
          "38"       Camelina
          "39"       Buckwheat

 Raster
 Attribute Domain Values and Definitions: CROPS 41-60

 Categorization Code   Land Cover
          "41"       Sugarbeets
          "42"       Dry Beans
          "43"       Potatoes
          "44"       Other Crops
          "45"       Sugarcane
          "46"       Sweet Potatoes
          "47"       Misc Vegs & Fruits
          "48"       Watermelons
          "49"       Onions
          "50"       Cucumbers
          "51"       Chick Peas
          "52"       Lentils
          "53"       Peas
          "54"       Tomatoes
          "55"       Caneberries
          "56"       Hops
          "57"       Herbs
          "58"       Clover/Wildflowers
          "59"       Sod/Grass Seed
          "60"       Switchgrass

 Raster
 Attribute Domain Values and Definitions: NON-CROP 61-65

 Categorization Code   Land Cover
          "61"       Fallow/Idle Cropland
          "62"       Pasture/Grass
          "63"       Forest
          "64"       Shrubland
          "65"       Barren

 Raster
 Attribute Domain Values and Definitions: CROPS 66-80

 Categorization Code   Land Cover
          "66"       Cherries
          "67"       Peaches
          "68"       Apples
          "69"       Grapes
          "70"       Christmas Trees
          "71"       Other Tree Crops
          "72"       Citrus
          "74"       Pecans
          "75"       Almonds
          "76"       Walnuts
          "77"       Pears

 Raster
 Attribute Domain Values and Definitions: OTHER 81-109

 Categorization Code   Land Cover
          "81"       Clouds/No Data
          "82"       Developed
          "83"       Water
          "87"       Wetlands
          "88"       Nonag/Undefined
          "92"       Aquaculture

 Raster
 Attribute Domain Values and Definitions: NLCD-DERIVED CLASSES 110-195

 Categorization Code   Land Cover
         "111"       Open Water
         "112"       Perennial Ice/Snow
         "121"       Developed/Open Space
         "122"       Developed/Low Intensity
         "123"       Developed/Med Intensity
         "124"       Developed/High Intensity
         "131"       Barren
         "141"       Deciduous Forest
         "142"       Evergreen Forest
         "143"       Mixed Forest
         "152"       Shrubland
         "171"       Grassland Herbaceous
         "181"       Pasture/Hay
         "190"       Woody Wetlands
         "195"       Herbaceous Wetlands

 Raster
 Attribute Domain Values and Definitions: CROPS 195-255

 Categorization Code   Land Cover
         "204"       Pistachios
         "205"       Triticale
         "206"       Carrots
         "207"       Asparagus
         "208"       Garlic
         "209"       Cantaloupes
         "210"       Prunes
         "211"       Olives
         "212"       Oranges
         "213"       Honeydew Melons
         "214"       Broccoli
         "216"       Peppers
         "217"       Pomegranates
         "218"       Nectarines
         "219"       Greens
         "220"       Plums
         "221"       Strawberries
         "222"       Squash
         "223"       Apricots
         "224"       Vetch
         "225"       Dbl Crop WinWht/Corn
         "226"       Dbl Crop Oats/Corn
         "227"       Lettuce
         "229"       Pumpkins
         "230"       Dbl Crop Lettuce/Durum Wht
         "231"       Dbl Crop Lettuce/Cantaloupe
         "232"       Dbl Crop Lettuce/Cotton
         "233"       Dbl Crop Lettuce/Barley
         "234"       Dbl Crop Durum Wht/Sorghum
         "235"       Dbl Crop Barley/Sorghum
         "236"       Dbl Crop WinWht/Sorghum
         "237"       Dbl Crop Barley/Corn
         "238"       Dbl Crop WinWht/Cotton
         "239"       Dbl Crop Soybeans/Cotton
         "240"       Dbl Crop Soybeans/Oats
         "241"       Dbl Crop Corn/Soybeans
         "242"       Blueberries
         "243"       Cabbage
         "244"       Cauliflower
         "245"       Celery
         "246"       Radishes
         "247"       Turnips
         "248"       Eggplants
         "249"       Gourds
         "250"       Cranberries
         "254"       Dbl Crop Barley/Soybeans
Distribution_Information:
Distributor:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: USDA, NASS Customer Service
Contact_Person: USDA, NASS Customer Service Staff
Contact_Address:
Address_Type: mailing and physical address
Address: 1400 Independence Avenue, SW, Room 5038-S
City: Washington
State_or_Province: District of Columbia
Postal_Code: 20250-9410
Country: USA
Contact_Voice_Telephone: 800-727-9540
Contact_Facsimile_Telephone: 703-877-8044
Contact_Electronic_Mail_Address: HQ_RDD_GIB@nass.usda.gov
Contact_Instructions:
Please visit the official website <http://www.nass.usda.gov/research/Cropland/SARS1a.htm> for distribution details. The Cropland Data Layer is available free for download at <http://nassgeodata.gmu.edu/CropScape/> and <http://datagateway.nrcs.usda.gov/>. Distribution issues can also be directed to the NASS Customer Service Hotline at 1-800-727-9540.
Resource_Description: Cropland Data Layer - Illinois 2000
Distribution_Liability:
Disclaimer: Users of the Cropland Data Layer (CDL) are solely responsible for interpretations made from these products. The CDL is provided 'as is' and the USDA, NASS does not warrant results you may obtain using the Cropland Data Layer. Contact our staff at (HQ_RDD_GIB@nass.usda.gov) if technical questions arise in the use of the CDL. NASS does maintain a Frequently Asked Questions (FAQ's) section on the CDL website at <http://www.nass.usda.gov/research/Cropland/SARS1a.htm>.

Standard_Order_Process:
Digital_Form:
Digital_Transfer_Information:
Format_Name: GEOTIFF
Format_Version_Date: Illinois 2000
Format_Information_Content: GEOTIFF
Transfer_Size:
The image file size will vary depending on the state and completeness of coverage. The user can specify the state, or a user-defined area of interest, and year(s) of CDL data to download at the Cropscape website <http://nassgeodata.gmu.edu/CropScape/>.
When downloading the data through the Geospatial Data Gateway <http://datagateway.nrcs.usda.gov/> all available years of CDL production for the requested state are included in one compressed file. Technical restrictions do not allow us to offer the CDL by individual state/year through the Geospatial Data Gateway. See the 'Ordering Instructions' section of this metadata file for additional information.
Digital_Transfer_Option:
Online_Option:
Computer_Contact_Information:
Network_Address:
Network_Resource_Name: <http://nassgeodata.gmu.edu/CropScape/>
Access_Instructions:
The CDL is available online and free for download from the Cropscape website <http://nassgeodata.gmu.edu/CropScape/>. It is also available free for download from the Geospatial Data Gateway website <http://datagateway.nrcs.usda.gov/>. See the 'Ordering Instructions' section of this metadata file for detailed Geospatial Data Gateway download instructions.
Fees:
Please visit the official website <http://www.nass.usda.gov/research/Cropland/SARS1a.htm> for distribution details. The Cropland Data Layer is available free for download at <http://nassgeodata.gmu.edu/CropScape/> and <http://datagateway.nrcs.usda.gov/>. Distribution issues can also be directed to the NASS Customer Service Hotline at 1-800-727-9540.
Ordering_Instructions:
The CDL is available online and free for download from the Cropscape website <http://nassgeodata.gmu.edu/CropScape/>. The Cropland Data Layer is also available free for download from the NRCS Geospatial Data Gateway at <http://datagateway.nrcs.usda.gov/>.

IMPORTANT NOTE: When downloading the CDL using the NRCS Geospatial Data Gateway all available years of CDL production for the requested state are included in a single compressed file. Geospatial Data Gateway technical restrictions do not allow us to offer the CDL by individual state/year. We are working on offering this option in the future. 
Instructions for downloading from the NRCS Geospatial Data Gateway:

Start by clicking on 'Get Data'

Then click on 'Quick State'

Scroll down to choose your state and click 'Continue'

Choose 'Land_use_land_cover' and select 'Cropland Data Layer by State' and 'Continue to Step3'

Choose 'Continue' to Step4

Lastly, you are given the option to download the data for free.
Custom_Order_Process:
For a list of other states and years of available CDL data please visit <http://nassgeodata.gmu.edu/CropScape/> or <http://www.nass.usda.gov/research/Cropland/SARS1a.htm>. Distribution issues can also be directed to the NASS Customer Service Hotline at 1-800-727-9540.
Technical_Prerequisites:
If the user does not have software capable of viewing GEOTIF (.tif) or ERDAS Imagine (.img) file formats then we suggest using the Cropscape website <http://nassgeodata.gmu.edu/CropScape/> or using the freeware browser ESRI ArcGIS Explorer <http://www.esri.com/>.
Metadata_Reference_Information:
Metadata_Date: 20120131
Metadata_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: USDA, NASS, Spatial Analysis Research Section
Contact_Person: USDA, NASS, Spatial Analysis Research Section Staff
Contact_Address:
Address_Type: mailing and physical address
Address: 3251 Old Lee Highway, Room 305
City: Fairfax
State_or_Province: Virginia
Postal_Code: 22030-1504
Country: USA
Contact_Voice_Telephone: 703-877-8000
Contact_Facsimile_Telephone: 703-877-8044
Contact_Electronic_Mail_Address: HQ_RDD_GIB@nass.usda.gov
Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata
Metadata_Standard_Version: FGDC-STD-001-1998
Metadata_Access_Constraints: No restrictions on the distribution or use of the metadata file
Metadata_Use_Constraints: No restrictions on the distribution or use of the metadata file
Generated by mp version 2.9.12 on Fri Jan 27 20:45:10 2012