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U.S. Department of Agriculture National Agricultural Statistics Service Research and Development Division |
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U.S. Department of Agriculture National Agricultural Statistics Service Research and Development Division |
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Cropland Data Layer Frequently Anticipated Questions CropScape Details Distribution Technical Details Previously Asked User Questions CropScape What data is hosted on the CropScape website? The geospatial data product called the Cropland Data Layer (CDL) is hosted on CropScape. The website is http://nassgeodata.gmu.edu/CropScape/. Currently, all historical products are hosted, available for use and free for download through CropScape. The CropScape website now offers a cultivated data layer called the "Crop Mask Layer". This cultivated crop mask data layer has a 30 meter spatial resolution and covers the continental United States. It is based on Cropland Data Layers from 2007 through 2011 with plans to update this crop mask data layer annually. The crop mask data layer and an accompanying document detailing the methodology are available for download at http://www.nass.usda.gov/research/Cropland/Release/. What new functional capabilities and enhancements were made to CropScape for the January 31, 2012 release?
The following list summarizes the new functional capabilities and enhancements that were made to CropScape for the January 31, 2012 release: The George Mason University group responsible for creating CropScape developed standard Web service for invocations or workflow in other web geospatial applications available at http://nassgeodata.gmu.edu:8080/axis2/services/CDLService?wsdl. There are 7 operations, including GetCDLStat, GetCDLImage, GetCDLComp, GetCDLFile, GetCDLValue, ExtractCDLByValues, and GetCDLPDF. This Web service supports HTTP GET/KVP POST/XML and SOAP encoding. Click here (standard Web service examples) for examples of the HTTP GET requests. The George Mason University group responsible for creating the CropScape website offer an online developer's guide available at http://nassgeodata.gmu.edu/CropScape/devhelp/help.html. Is the CDL available as a web mapping service (WMS)? If not, is there any timeline in place to implement such a service?
The WMS is implemented and is available to the general public. It is OGC standard compliant. The CDL can be served as a data layer from the user's application. I’m having trouble finding the address of that service for use in my GIS application. Could you please direct me to a link that will work with ArcGIS 9.2?
Please use the following links: GetCapabilities and GetMap Example. Only EPSG:4326 the customized ESPG:102004 (USGS Albers) are supported in the GetMap Request now. Is there a way to view the Cropland Data Layer data on CropScape with just one or two commodities shown at the national, state, district and/or county levels?
To view the Cropland Data Layer data on CropScape with just one or two commodities shown at the national, state, district and/or county levels: 1) Select "Area of Interest by State/ASD/County" or by "Rectangle/Polygon/Circle" from the top icon tray 2) Select the "Area of interest statistics" from the top icon tray 3) Choose the commodity of interest from the popup, you can choose one or many 4) Export the selected crop, the individual crop should then display on a graphic. Our pixel counting algorithm is straightforward. We define an area of interest first, which is enclosed with a boundary. It is then rasterized and the pixels that fall within this AOI are counted. ArcGIS server is not used in this application. What differences can be expected when comparing CropScape pixel counts and official NASS statistics for counties, ASD, and states?
There will be differences between CropScape and official NASS estimates when comparing acreage statistics at the state, district, and county levels. Statistics generated by CropScape are dependent upon pixel counting. Pixel counting is usually downward biased when compared to the official estimates. Counting pixels and multiplying by the area of each pixel will result in biased area estimates and should be considered raw numbers needing bias correction. Official crop acreage estimates at the state and county level are available at http://www.nass.usda.gov/. CropScape allows users to analyze and interact with areas less than 2,000,000 square kilometers. However, CropScape allows for a national download by year. CropScape will implement map production/printing services and change detection/analysis between years sometime in the future. CropScape’s delivery of all historical geospatial data is meant to eliminate the need for DVD production. Beginning with the release of the 2011 CDL no further DVD/CD-ROM media will be available. All CDL data will be available from either CropScape or SARS webpages. Zoom to the national scale map, choose the year that you want to download and click on "download defined area of interest data" and respond yes to the download confirmation question. You will receive one Winzip compressed file of the year selected CDLs, and it will contain state level CDL's in GeoTIFF format. What should I do if I get an error message upon startup of CropScape stating "To perform all operations successfully, please download and install Adobe Flash Player plug-in in your browser"?
CropScape is optimized for use with Adobe Flash player. Please upgrade your Adobe Flash player at http://www.adobe.com/. ArcGIS Explorer Online only supports map, image and feature services from ArcGIS Server (http://help.arcgis.com/en/arcgisonline/help/index.html#/Creating_maps/010q0000001n000000/ADDING_LAYERS).
For ArcGIS Explorer, CDL WMS could be added as one layer from GIS services. You can access the CDL WMS at http://129.174.131.6/cgi-bin/wms_cdlall?. You could learn how to add a legend of a WMS layer in ArcGIS Explorer Desktop at http://webhelp.esri.com/arcgisexplorer/900/en/legend_window.htm. Currently, we do not define the legend as a sublayer of CDL layers in our CDL WMS, so the legend for your selected CDL layers could not be displayed like the guide suggests. But you still could try to access the legend by sending a request: http://129.174.131.6/cgi-bin/wms_cdlall?version=1.0.0&service=wms&request=getlegendgraphic&layer=cdl_2009&format=image/png You can generate a kml file for the CDL data of the area of interest in CropScape, then add the kml file as one layer in ArcGIS Explorer Desktop, then right click data layer, and select "Show Popup", and the legend will be shown in the popup window. If you are using Microsoft Internet Explorer, try changing the default timeout value (greater than 100000ms if your network connection is slow). Here is a link detailing how to change the default timeout value: http://support.microsoft.com/kb/813827. You could also try using a web browser other than Internet Explorer, such as Firefox or Google Chrome. The direct URL for the compressed CDL file for each year is http://129.174.131.228/nass_data_cache/tar/*_cdls.tar.gz (where * is the year, for example "2011_cdls.tar.gz"). The user could input the direct URL into the browser or downloading software to obtain them. What should I do when I get a CropScape error downloading certain states or when I get a pop up window that says scripts are running on this website which may make my computer unresponsive?
This issue is caused by security controls of Internet Explorer when rendering a state with a large boundary file, which can take a long time depending on your internet connection speed. There are three possible solutions:
Solution 1. If you get a window that says "...Do you want to abort the script?", click the "NO" button to continue. Has someone compiled all of the exported CDL attribute tables by year and state into a master spreadsheet?
The 2012 accuracy data is available at CropScape_2012_Stats.xls.
The 2012 data is available at http://www.nass.usda.gov/research/Cropland/docs/CDL_2012_accuracy_assessments.zip. The CDL .tif file contains the category values but not the category names. For ESRI’s ArcGIS ArcMap application to display the category names, download the file: generic_cdl_attributes.tif.vat.dbf. This generic file contains all possible CDL colors and category names. As long as the .tif file and the .tif.vat.dbf file have the same file name, then the category names will load automatically in ArcMap. So change the file name (not extension) of the generic_cdl_attributes.tif.vat.dbf to match the file name of the downloaded CDL .tif file. Then add the .tif file as a layer in ArcMap. The category names will display in the Table of Contents window. I have downloaded a user-defined subset of the Cropland Data Layer from CropScape. I am using ArcGIS to view my download, but there is no histogram information in the attribute table. How do I generate the statistics for my downloaded area in ArcGIS?
To create a pixel "count" field in the attribute table of the downloaded CDL use the "Build Raster Attribute Table" Function in ESRI ArcGIS. In ESRI ArcGIS Version 9.3 this function is located at ArcToolbox > Data Management Tools > Raster > Raster Properties > Build Raster Attribute Table. Specify the downloaded CDL tif file as the Input Raster and accept all other defaults and click OK. After it has run successfully, a new "Count" data field is added to the attribute table. Count represents a raw pixel count. To calculate acreage multiple the count by the square meters conversion factor which is dependent upon the CDL pixel size. The conversion factor for 30 meter pixels is 0.222394. The conversion factor for 56 meter pixels is 0.774922. I am using Erdas Imagine to view the data that I downloaded from CropScape, but there is no histogram information or category names. How do I build statistics in Erdas Imagine?
To generate statistics in Erdas Imagine, go to Tools > Image Information then click on "Compute the statistics." If you have the TIF file open in a Viewer, then you will have to close it and reopen the TIF file. Now when you view the attribute information, there should be a Histogram column, which represents the pixel count per category. To calculate acreage multiple the count by the square meters conversion factor which is dependent upon the CDL pixel size. The conversion factor for 30 meter pixels is 0.222394. The conversion factor for 56 meter pixels is 0.774922. You first must build statistics for the TIF file as outlined in the question above. To add category names, open the TIF in a Viewer and select Raster > Attributes. In the Raster Attribute Editor select Edit > Add Class Names. This new "Class Names" column can be populated manually or you can download this prepared DAT file located at: http://www.nass.usda.gov/research/Cropland/docs/cdl_class_names.zip. Unzip the DAT file and save it to your computer. Then in the Raster Attribute Editor highlight the "Class Names" column by left-clicking on the header of the Class Names column. Then right-click on the Class Names column and select the Import option. Specify the DAT file as the file to import and this will add all possible CDL class names to your TIF attribute table. To add the standard CDL colors to an Erdas Imagine attribute table, follow the instructions above except use this prepared cdl_colors.data file: http://www.nass.usda.gov/research/Cropland/docs/cdl_colors.zip. You will need to write JavaScript code using the Bing Map API to add a kml layer, please follow the instructions at: http://msdn.microsoft.com/en-us/library/cc316942.aspx. When adding the CDL WMS to ArcGIS Explorer or ArcCatalog, I get an error message saying "Invalid Format for Exception Parameter at WMS 1.3.0". How do I correct this?
First, you can access the CDL WMS at: http://129.174.131.6/cgi-bin/wms_cdlall?. But the default WMS GetCapabilities request in ArcGIS Explorer or ArcCatalog is at version 1.3.0 with EXCEPTIONS=application/vnd.ogc.se_xml, which is not standard format (XML, INIMAGE or BLANK), so the error message will be displayed. You can try changing the WMS version from default 1.3.0 to 1.1.0 when adding to the WMS server. For example screenshots, click here (AddWMS.jpg) and here (Preview.jpg).. The following downloadable jpeg image files are color legends by year for the Contentintal United States CDLs:
Distribution Is the CDL data available during the growing season? Will this data be available anywhere as it is being compiled, or do we have to wait until January for data release?
The CDL is considered confidential and market sensitive during the growing season and we cannot release it until after NASS' official year end area county estimates are published. Furthermore, the CDL is considered preliminary during the growing season and could be misleading to our customers, as we continue to receive updated ground truth and satellite imagery throughout the season. What is the preferred citation for the Cropland Data Layer and CropScape? USDA National Agricultural Statistics Service Cropland Data Layer. {YEAR}. Published crop-specific data layer [Online]. Available at http://nassgeodata.gmu.edu/CropScape/ (accessed {DATE}; verified {DATE}). USDA-NASS, Washington, DC. Where can I obtain the Cropland Data Layer (CDL) and what is the cost? The entire inventory of CDL products are available free at http://nassgeodata.gmu.edu/CropScape/ and are also free for download through the USDA NRCS Geospatial Data Gateway. 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 WinZIP file. Geospatial Data Gateway technical restrictions do not allow us to offer the CDL by individual state/year. The zip file will include all years of CDL data for the requested state in a GeoTIFF (.tif) file format projected in UTM, along with the accompanying metadata, accuracy assessment information and image legend. Below are instructions for downloading from the NRCS Geospatial Data Gateway (http://datagateway.nrcs.usda.gov/):
1. Go to website: http://datagateway.nrcs.usda.gov/ The CDL program became operational with one state in 1997. CDL coverage prior to 2008 is listed, with 2008 providing the first national annual coverage. Please visit the SARS website for a list of all states and years of available CDL data. The CDL data is available in a GeoTIFF (.tif) file format. The GeoTIFF for a single CDL data layer will have three files associated with it: .tif, .tfw, and .aux. Older CDLs may also be available in an ERDAS Imagine (.img) file format. The Erdas Imagine file will have two files associated with it: .img and .rrd. The CDL is processed using a Albers Equal-Area Conic Projection with a spheroid of GRS 1980 and datum of NAD83. The downloadable zip files from the SARS website and http://nassgeodata.gmu.edu/CropScape/ are offered in the Albers projection. In order to conform to the Geospatial Data Gateway requirements, the CDL is reprojected from Albers to the dominant Universal Transverse Mercator (UTM) zone with a spheroid and datum of WGS84. The one exception to UTM is for
Wisconsin. Wisconsin is projected using the Wisconsin Transverse
Mercator (WTM) projection. This WTM projection is based on the 1991
adjustment to NAD83, and is called WTM83/91. Projection parameters and
additional information about WTM83/91 is posted on the DNR
website: http://www.dnr.state.wi.us/maps/gis/wtm8391.html. If you already have GIS capability, you should have no trouble working with the CDL datasets. If you do not have software capable of viewing Geotiff (.tif) file format then we suggest using the freeware browser ESRI ArcReader. Some users have reported issues with viewing the CDL using ENVI software. NASS suggests using the GeoTIFF file format with ENVI and ensuring that the three associated files (.tif, .tfw, and .aux) are all kept together. ENVI version 4.4/ENVI Zoom now will open the CDL without issue. Originally, field preparation and digitizing work were performed in NASS Field Offices, and the remote sensing analysis performed by the Remote Sensing Section later called the Spatial Analysis Research Section (SARS) of NASS. However, in 1997 SARS entered into a data sharing partnership with USDA's Foreign Agricultural Service and USDA's Farm Service Agency. The agreement provided access to Landsat 5 coverage in the states selected for the project by SARS. The first states covered with the data sharing partnership were Arkansas, North Dakota and South Dakota. Improvements in hardware along with software enhancements made program expansion possible for the 1999 growing season. NASS Research & Development Division solicited additional states to find outside cooperators/partners to provide an analyst and hardware to perform duties associated with the Acreage Estimation Program. The Illinois and Mississippi State Field Offices were able to obtain partnership agreements with external State/Federal Agencies. For crop year 2000, the states of Iowa and Indiana were added to the Program. North Dakota was able to obtain a partner for the 2000 crop year cooperatively with NDSU through an EPA water quality grant for 5 years. Indiana was added to the program for crop year 2000 also, but as a regional type center where the ground data collection, and digitization was performed at the Indiana State Office, and the acreage estimation was performed at the Illinois State Office. For crop year 2001, the Missouri boot heel area was added to the program. All boot heel digitizing was performed by the Missouri Ag Statistics Service, and image processing duties were performed by the Arkansas Ag Statistical Service. Nebraska and Wisconsin were added as pilot states, where all digitizing was performed by the Nebraska and Wisconsin Ag Statistics Service offices respectively, and image processing functions were performed by SARS. Maryland/Delaware were also added as a pilot program where digitizing was done by the Univ. MD Mid-Atlantic RESAC group, and image processing was performed by the SARS group. For crop year 2002, Nebraska expanded to full state coverage, and Wisconsin expanded to full state coverage in 2003. The 2002 10 State Mid-Atlantic based Cropland Data Layer product was sponsored in part by a NASA/Raytheon/Synergy Project through Towson University, with the digitizing and image analysis performed under contract by NASS. The Mid-Atlantic CDL products were based on the 2002 June Agricultural Survey and the Agriculture Coverage Evaluation Survey (ACES) that coincided with the 2002 Agricultural Census. For crop year 2004, the IRS Resourcesat-1 AWiFS sensor was used over Nebraska, Indiana and Arkansas to perform acreage analysis. The AR, IN and NE CDL's were released with both Landsat TM classifications as well as AWiFS classifications. The AWiFS sensor has 56 meters multispectral resolution, and five day repeat coverage. The best possible scene dates taken during the month of August 2004 were used to create the AWiFS CDL products. The AWiFS scenes were orthorectified to a resampled EarthSat GeoCover base of 56 meters. A Florida CDL for 2004 was released in February of 2007 using Landsat 5/7 imagery. The Florida CDL was the first CDL created exclusively with See5, and it was the first usage of the segmentation based gap filled Landsat-7 SLC-off imagery. It included the first usage of the Farm Service Agency/Common Land Unit and the Florida Citrus Grove layer for ground truth training. A cooperative partnership between Univ. of MD/Dept of Geography and SARS helped process the Louisiana 2004 CDL. For crop year 2005, the Idaho Cropland Data Layer was created with a cooperative partnership between a Utah State University, the United Potato Growers of Idaho and NASS. This partnership produced both a Landsat TM and Resourcesat-1 AWiFS classification over the Idaho Snake River Plain. The 2005 Midwestern CDL update, contained new AWiFS classifications and a revised Wisconsin TM based classification. The new AWiFS classifications cover Nebraska and North Dakota. The Wisconsin revision was performed under contract for the Wisconsin State, Bureau of Environmental & Occupational Health and Department of Health and Family Services. The Wisconsin CDL is now a complete statewide classification that is nearly cloud free, additional small acreage crops are identified and the non-ag land uses across the state are better defined. The 2005 Mississippi Delta CDL product contains four states: Arkansas, Louisiana, Mississippi and the Missouri (bootheel). This is truly a unique product where the intensely cultivated Delta Region was classified using regression tree classifier See5.0 available from www.rulequest.com over the 2001 NLCD defined mapping Zone 45 http://www.mrlc.gov/ for the States of Arkansas, Louisiana and Missouri. The Zone 45 classification results from See5.0 were overlaid on top of the Arkansas, Louisiana and Missouri bootheel, resulting in an accurate ag classification and an enhanced non-ag land use classification leveraging results from the 2001 NLCD products. The traditional pixel based PEDITOR classification covers the remaining parts of these states. Additionally, 2005 AWiFS classifications of these four states are provided as well. The 2006 Delta/Midwestern/Pacific Northwest CDL products covered eleven states: AR, IL, IN, IA, LA, MO, MS, NE, ND, WA, WI. Illinois and Indiana were processed with Peditor. The remaining States were processed using See5 decision tree software. The Mississippi Delta CDL and the remaining Midwestern and Prairie States were processed exclusively with See5 using the FSA Common Land Unit for ground truth. The 2007 CDL product became operational in NASS delivering for the first time in-season acreage estimates for the October 2007 Crop Report across all speculative corn and soybean states. Twenty-one states total (AR, CA, IL, IN, IA, ID, KS, LA, MI, MN, MO, MS, MT, ND, NE, OH, OK, OR, SD, WA, WI) were processed into CDL's, a new record for the program. Additionally, new CDL's were created for crop year '06 for KS, MN, MO, OH, OK, SD. Michigan State University/Land Policy Institute entered into a cooperative partnership with SARS obtained funding to provide an image analyst to process Michigan. The 2008 crop year produced real-time CDL acreage estimates for the June Ag Survey for winter wheat, the August Crop Report and the October Crop Report for corn and soybeans. Eighteen states (AR, CO, IA, IL, IN, KS, LA, MI, MN, MO, MS, OH, OK, ND, NE, SD, TX, WI) were processed during the crop year with additional CDL production possible over the Southeastern and Southwestern US. The 2009 crop year produced real-time CDL acreage estimates for the June Ag Survey and September Small Grain Summary for winter wheat, the August, September and October Crop Reports for corn, soybeans, rice and cotton. 2009 was the inaugural year for coverage of the 48 continental US states. The 2009 product was released at 56 meters resolution. The 2010 CDL product was released the first week of January 2011 co-incident with CropScape. The 2010 product utilized Landsat TM/ETM+ and AWiFS imagery for production of a 30m national product. The 2011 CDL product was released January 31, 2012. The 2011 product utilized Deimos-1, UK-DMC 2, Landsat TM/ETM+, and AWiFS imagery for production of a 30m national product. Coincident with the release of the 2011 product, the entire historical CDL catalog was re-released with minor category code and class name revisions. These revisions were done to eliminate redundant or unused categories. Please view the crosswalk document for a detailed listing of the revisions. The 2012 CDL product was released January 31, 2013. The 2012 product utilized Deimos-1, UK-DMC 2, and Landsat TM/ETM+ imagery for production of a 30m national product. The CDL was created as an offshoot of the Acreage Estimation Program, which was historically used for its statistical methodology and ability to derive acreage estimates. Functionality was extended to GIS mapping in the late 1990's. The CDL product provides orthorectified data for agribusiness and researchers in the GIS and remote sensing communities. The entire inventory of CDL products are available free at http://nassgeodata.gmu.edu/CropScape/ and are also free for download through the USDA NRCS Geospatial Data Gateway. The most recent CDL products are available free for download for a limited time through the USDA NASS Cropland Data Layer website. Yes, the NASS Cropland Data Layer has no copyright restrictions. The CDL is considered public domain and free to redistribute. However, NASS would appreciate acknowledgment for the usage of our CDL product. Metadata for the entire CDL inventory is stored online by state and year. The metadata is created from software produced by the USGS and can be found at http://geology.usgs.gov/tools/metadata/. The metadata files contain information on the sensor types, dates of observation, and the accuracy statistics, such as percent correct, user and producer accuracy and kappa coefficients. The accuracy statistics are for agricultural land cover classes only. The accuracy of the non-agricultural land cover classes within the Cropland Data Layer are entirely dependent upon the USGS, National Land Cover Dataset (NLCD). We recommend that users consider the NLCD for studies involving non-agricultural land cover. For more information please reference the NLCD. Please visit the NASS CDL website for updates on the proposed CDL states for the upcoming year. A national CDL is currently planned for crop year 2013. Additionally, NASS is working with the USGS, National Land Cover Dataset (NLCD) Program on the 2011 NLCD mapping endeavor, with the intent on providing agricultural input into their mapping process. Distribution issues can be directed to the NASS Customer Service Hotline at 1-800-727-9540. Content questions can be directed to the NASS Spatial Analysis Research Section (SARS) at 703-877-8000 or email HQ_RDD_GIB@nass.usda.gov.
Technical Details The classification process used to create the CDL prior to 2006 was based on a maximum likelihood classifier approach using an in-house software package. The CDL relied mainly on data from the Landsat TM/ETM satellite which had a 16-day revisit. And the in-house software limited the use of only two scenes per classification. The only available ground truth was through the NASS June Area Survey (JAS). The JAS data was collected by field enumerators so it was fairly accurate but was limited in coverage due to the cost and time constraints of such a massive survey. It was also very labor intensive to digitize and label all of the collected field data for use in the classification process. Non-agricultural land cover was based solely on image analyst interpretation. Beginning in 2006, we began using a new satellite sensor, new software, more extensive training/validation data, and began using the NLCD to help identify non-agricultural land cover. The in-house software was phased out in favor of a commercial software suite. This improved processing efficiency and, more importantly, allowed for unlimited classification inputs. Combined with the rapid revisit of the AWiFS satellite sensor, this has nearly eliminated cloud contamination issues that plagued the CDL products prior to 2006. The new satellite is the AWiFS sensor that is on the Resourcesat-1 satellite. It has a resolution is 56 meters, or .77 acres, and revisits the same area approximately every 5 days. We are now collecting AWiFS data year round and supplement the CDL classification process with MODIS data. We now use USDA Farm Service Agency (FSA) Common Land Unit (CLU) data for training our classifier in the agricultural domain. We use the most current USGS NLCD dataset to train over the non-agricultural domain. The new methodology uses a decision tree classifier as opposed to the maximum likelihood classifier. Decision trees offer several advantages over the more traditional maximum likelihood classification method. The advantages include being: 1) non-parametric by nature and thus not reliant on the assumption of the input data being normally distributed, 2) efficient to construct and thus capable of handling large and complex data sets, 3) able to incorporate missing and non-continuous data, and 4) able to sort out non-linear relationships. Prior to the 2006, the CDL processing was done entirely with in-house maintained software called PEDITOR. The PEDITOR classification was based on a maximum likelihood classifier. Limitations to the software also made it impossible to use more than two satellite scenes per classification, which was a significant hindrance when trying to minimize cloud coverage. Beginning with the 2006 CDL products, the CDL program phased out the use of PEDITOR and transitioned to a commercial software suite. Leica Geosystems ERDAS Imagine is used in the pre- and post- processing of all raster-based data. ESRI ArcGIS is used to prepare the vector-based training and validation data. Rulequest See5.0 is used to create a decision tree based classifier. The NLCD Mapping Tool is used to apply the See5.0 decision-tree via ERDAS Imagine. The CDL Program uses medium resolution satellites. CDL products prior to 2006 relied primarily on Landsat 4/5/7. Beginning with the 2006 CDL products, the CDL program transitioned to using the sensor on the IRS-P6 Resourcesat-1 satellite. Currently, it is too costly to use higher resolution satellites to perform crop acreage estimation over large areas. Beginning in 2006, the MODIS, 250 meter resolution 16-day composite Normalized Difference Vegetation Index (NDVI) from the NASA Terra satellite is used as an ancillary input to the CDL classification process. Additionally, the USGS policy of opening up the Landsat archive for free access in 2009 delivered the potential for the CDL to deliver in-season and national level agricultural monitoring capability. The 2011 CDL program added two additional sensors, the Deimos-1 and the UK-DMC 2. Detailed accuracy assessment tables are published within the official metadata files. Generally, the dominant agricultural crop types have accuracies ranging from mid 80% to mid 90%. Western Arkansas and Northern Missouri were not fully covered in the program until crop year 2006. Cloud coverage, during any given year, may limit the extent of the area coverage. However, beginning in crop year 2006, the CDL Program transitioned from using the Landsat TM/ETM satellite to AWiFS. The high revisit rate of the AWiFS sensor has reduced issues with cloud coverage so most CDL states will be cloud-free and full state coverage where possible. Prior to 2006, the Landsat TM/ETM categorized images were co-registered to MDA/EarthSat Inc's ortho-rectified GeoCover Stock Mosaic images using automated block correlation techniques. The resulting correlations were applied to each categorized image and then added to a master image or mosaic using NASS' in-house software, PEDITOR. The GeoCover Stock Mosaics are within 50 meters root mean squared error overall. See MDA/EarthSat's http://www.mdafederal.com/home website for further details. The AWiFS images purchased beginning in 2005 were all orthorectified by GeoEye, so NASS does not ortho-correct the AWiFS-based raw imagery. The CDL retains the input imagery's positional accuracy of 60 meters at the circular error at the 90 percent confidence level (CE90). CE90 is a standard metric often used for horizontal accuracy in map products and can be interpreted as 90% of well-defined points tested must fall within a certain radial AWiFS distance. The following presentations related to the spatial accuracy of the imagery were presented at the 2007 FAS PECAD Seminar by Mary Pagnutti and Gyanesh Chander. The DEIMOS-1 and UK-DMC2 imagery used in the production of the Cropland Data Layer is orthorectified to a radial root mean square error (RMSE) of approximately 10 meters. Distribution issues can be directed to the NASS Customer Service Hotline at 1-800-727-9540. Content questions can be directed to the NASS Spatial Analysis Research Section (SARS) at 703-877-8000 or email HQ_RDD_GIB@nass.usda.gov.
Previously Asked User Questions The simple answer is no. As explained in the Program Methodology section, NASS adjusts the CDL results by using a regression estimator and ground gathered data from farm operators. The farmer reported data is strictly confidential and only available to NASS employees in a secure NASS facility. The regression estimates are only one input to official state and county crop acreage estimates. In addition to regression estimates, NASS staff use the results of farmer reported data from surveys, Farm Service Agency data where available, agri-business data and the Census of Agriculture data. Thus, the official estimate is the single best number that NASS can come up with giving all of the inputs some representation. The one major advantage of the classified data is that it is available at a geographic level well below the county level. However, it is possible to pixel count and return acreage numbers close to the official estimate, but pixel counting does not account for cloud covered areas as well as the inaccuracies associated with a pixel based classification. How are fields with multiple crop types planted in the same season handled in the Cropland Data Layer, such as late season cover crops or winter wheat followed by soybeans?
The primary focus of the Cropland Data Layer (CDL) is on large area summer crops. The Farm Service Agency CLU data is our source of agricultural training data for the CDL classifier. We depend on the data that the farmer reports on their FSA/CLU signup forms. The ground truth is prepared to show whether a single/double crop was planted in a particular field. So, if a single use winter wheat field was under production for a given year, than one ww field will show up in the CDL. A winter wheat crop planted in the Fall of 2009 will be identified in the 2010 CDL, as we consider the time of harvest as the current year of production. If the field is multi-use during a given year, for example winter wheat (ww) followed by soybeans (sb), then a double cropping situation exists and the category for that given field will be ww/sb, and is indicated as such in the legend. If a field is only sb during that year, then it will be identified as sb only. Therefore, all major crop rotations/patterns are captured with this method and are consider mutually exclusive for a given pixel/field. We do not monitor the fruit and vegetable winter industry (i.e., Florida/California), as we focus primarily on the large area summer crops and are not equipped to monitor triple or quad cropping practices. Please reference the official metadata for a complete list of all possible CDL categories, including valid double-crop categories. NASS
says this is a Cropland data layer product, what about the areas that
are not agriculturally intensive?
The strength of the CDL is in its agricultural classifications. Due to the extensive agricultural training data provided by the FSA, CLU Program, the major crop types for a CDL state will normally have a classification accuracy of 85% to 95%. However, the FSA CLU data does not contain much, if any, non-agricultural data. The only source of non-ag training available at the scale required to meet the needs of the CDL Program is the USGS National Land Cover Dataset (NLCD). We sample the non-ag categories of the NLCD proportionate to the available FSA CLU data for a state and include this in the CDL classification process. Thus, the accuracy of the non-agricultural land cover classes within the Cropland Data Layer are entirely dependent upon the NLCD. We recommend that users consider the NLCD for studies involving non-agricultural land cover. For more information please reference the NLCD. The FSA CLU data does contain a small amount of nonagricultural data and this nonag FSA data was used in the classification process. Thus, there are some 2007 CDL states that may have multiple categories for the same nonag land cover type, such as category 87 (FSA-sampled wetland) and category 190 and 195 (NLCD-sampled wetlands). This is should only be an issue in the 2006 and 2007 CDL products. Beginning in 2008, the use of the FSA CLU non-ag for classification training was discontinued. Prior to 2006, the field level training data was collected solely through the June Agricultural Survey (JAS). The JAS is an annual national survey of randomly selected areas of land. 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 making it difficult to know what specific type of land use/cover actually is on the ground. Thus, non-agricultural land cover contained within the 2005 and older CDL products were based solely on an individual analyst’s best interpretation. Does
the CDL differentiate between grassland types such as pasture, urban
grassland, CRP grassland and other grass-related land cover types?
Unfortunately, the grassland-related categories have traditionally had very low classification accuracy in the CDL. This is an issue of land use versus land cover. The satellite sensor and classification process can only identify land cover types. It cannot differentiate specific land uses, such as urban open space, shrubland, pasture for grazing, or CRP. We continue to search for program enhancements and ancillary datasets that may help improve the identification of grassland and pasture categories within the CDL.
Differences in the CDL can also arise from the use of the NLCD Pasture/Hay category. We use Farm Service Agency (FSA) to identify the
ag land cover and the NLCD to identify the nonag. So, we ignore NLCD
code 82 (Cultivated Crops) during the CDL classification process. It is
left up to the individual analyst for a specific CDL state as to
whether or not to use the NLCD code 81 (Pasture/Hay). Typically, it is
used for training because there is not much pasture or hay available in
the FSA data in these areas. In states where there is a lot of
pasture/hay in the FSA data, such as the Great Plains States, then the
analysts typically ignore NLCD code 81 and rely entirely on the FSA
data to identify pasture/hay categories.
How
do I determine how much area of a certain crop is grown within a
certain radius of a given location?
A user can summarize the area of a certain crop within a certain radius, but they should be aware of the potential limitations of pixel counting. Most land cover classification datasets will contain some level of counting bias (typically downward). There is also the issue of potential cloud contamination or incomplete state coverage. All category codes, class names and legend colors are standardized and consistent for all states and all years of the Cropland Data Layer Program. The 2011 CDL was released on January 31, 2012. Coincident with this release was a re-release of the entire historical catalog of CDLs for the years 1997 through 2010. These re-releases contain updated category codes and class names. These revisions were done to eliminate redundant and/or unused categories. The majority of the changes apply to the nonagricultural domain. Please view the crosswalk document for a detailed listing of the revisions. There were no category or coding changes in the 2012 CDL product. Some users have reported issues with viewing the CDL using ENVI software. NASS suggests using the GeoTIFF file format with ENVI and ensuring that the three associated files (.tif, .tfw, and .aux) are all kept together. ENVI version 4.4/ENVI Zoom now will open the CDL without issue. Crop year 2008 was the first year a national CDL was produced. We are looking to continue national coverage through resource partnerships and hope to increase productivity through technological innovation. Beginning with crop year 2006, the CDL program covered all of the NASS speculative corn and soybean states, because of the newly developed program efficiencies, the large swath width and rapid repeat times of AWiFS, and the availability and coverage of the FSA Common Land Unit Program. Please visit the NASS CDL website for updates on the proposed CDL states for the upcoming year. The CDL Program remains focused on the major crops of the Midwest and Mississippi Delta regions: corn, soybeans, rice and cotton. We hope to continue annual national CDL production provided adequate human, satellite, and technological resources. A Microsoft Word document was created to provide step-by-step instructions on how to create a CDL legend using ArcGIS. The document is located at: http://www.nass.usda.gov/research/Cropland/docs/CDL_Create_Legend.doc. In general, no smoothing or filtering is done to the final CDL classification. However, there have been exceptions. There was no smoothing or filtering of any kind used in the 2012 CDL Program. The original 2006 CDL products did contain a small level of smoothing, but in March of 2009 all but one of the 2006 CDL products with were re-released with no smoothing. The one exception is the 2006 Washington CDL which still contains the smoothing. Smoothing has also been applied to cranberries in the 2008, 2009, 2010 and 2011 New England States and to oranges in 2008, 2009 and 2010 Florida. Please refer to the "Processing Description" Section of the official metadata files to find out if any smoothing was applied to a particular state or year. Please visit the Charts and Maps Section of the NASS website for information about other spatial datasets. Of particular note are the vegetation condition images, state land use strata, and crop progress charts. The Agricultural Statistics Districts (ASD) for the entire U.S. are available in ESRI shapefile format ASD shapefile. An ASD is defined as a contiguous group of counties having relatively similar agricultural characteristics. The ASD's used by NASS usually divide each state into as many as nine Agricultural Statistics Districts to make data comparison easier. Each district is more homogeneous with respect to agriculture than the state as a whole. The following link provides national State, ASD, and county codes in tabular .csv format asds2009.csv. Many NASS research reports are available online at the following website: http://www.nass.usda.gov/Education_and_Outreach/Reports,_Presentations_and_Conferences/Reports_by_Date/index.asp How do I add class names and/or histogram values
to the Geotiff file when viewing the CDL in ESRI ArcGIS software?
Older CDL Geotiff files (prior to 2006) do not have the class
names in the attribute tables. However, the attribute code values are defined within the associated metadata file.
The user can reference the metadata "Entity and Attribute Information" Section of the metadata file and can add the
class names manually if desired.
Distribution issues can be directed to the NASS Customer Service Hotline at 1-800-727-9540. Content questions can be directed to the NASS Spatial Analysis Research Section (SARS) at 703-877-8000 or email HQ_RDD_GIB@nass.usda.gov.
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