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USDA Establishes a Common Land Unit
By Jim Heald, Technical Coordinator for the Common Land Unit Project

As part of its effort to map the nation's farms and fields, the United States Department of Agriculture (USDA) has set out to establish the Common Land Unit (CLU) as a standardized GIS data layer that will allow mapping to be integrated easily on a nationwide basis. Along with its partner agencies, Rural Development and the Natural Resource Conservation Service (NRCS), the USDA's Farm Service Agency (FSA) is in the process of implementing desktop GIS at more than 2,500 field service center locations across the country. Ultimately, the GIS resources for the agency will be managed in a distributed database environment. As with many public agencies, the majority of FSA's business data contains geospatial components or is referenced to geographic locations (e.g., land records, field locations, and soil types).

The development of the CLU data layer is the most critical component for the successful implementation of GIS by the FSA. This layer will ultimately include all farm fields, rangeland, and pastureland in the United States. In conjunction with digital imagery and other data, FSA will use the CLU data layers to support farm service programs, monitor compliance, and respond to natural disasters.

The FSA faces several challenges in developing the CLU layer. The sheer size of the task is formidable. FSA wants to map all of the farm fields in the country or, at least, all the fields involved in agency programs. Because the data is constantly changing, as initial digitizing is completed data must be put into a maintenance program. In addition, the FSA needs to maintain tabular and geospatial time-series information and must address security and privacy issues. For example, farm and disaster payments are directly tied to acreage and crops reported by producers.

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As part of its effort to map the nation's farms and fields, the United States Department of Agriculture (USDA) has set out to establish the Common Land Unit (CLU) as a standardized GIS data layer that will allow mapping to be integrated easily on a nationwide basis.

The initial proposal to develop the CLU data layer outlined a process to transfer data from the hard-copy maps using heads-up (i.e., on-screen) digitizing on a digital orthophoto quadrangle (DOQ) base using ArcView 3.x in a Windows NT environment. FSA's Aerial Photography Field Office is responsible for delivering the DOQ to the digitizing centers. FSA made a policy decision to mosaic the DOQ to create seamless county images because image quality and edgematching problems made the raw DOQ unacceptable as a basemap for this project. The mosaics are tone balanced, and most common DOQ edgematching problems are eliminated. Seam lines are also adjusted where possible so that seams do not divide farm fields.

Currently, the Aerial Photography Field Office is delivering full-resolution TIF files tiled by quadrangle boundary and a county mosaic in MrSID compressed format. This will significantly reduce disk space requirements for new equipment and help the FSA accommodate other types of imagery.

By January 2000, 13 digitizing centers were established at field office locations in seven states. These offices are developing the CLU data layer using ArcView 3.x with customized digitizing and quality control extensions developed for the project. FSA proposes completion of the CLU layer for the entire country by fiscal year 2005, if not sooner.

Each state office, in cooperation with the partner agency NRCS, developed a priority list. These considerations also included the development of large contiguous blocks of counties within priority states to minimize the cost of mosaicking DOQ imagery and facilitate compliance activities using digital aerial photography and GIS. Factors considered by FSA in developing the priority list were

  1. The existing workload
  2. Availability of DOQ data
  3. Agricultural land and crop production levels
  4. Expertise and adaptability of county staff
  5. Availability of digital soil data

The GIS team believes that eliminating any need for hard-copy maps is the only way to ensure a successful transition to GIS within FSA. One of the major hurdles in eliminating hard-copy maps was the crop reporting and compliance process. Every growing season, producers report their growing intentions (i.e., types of crops and number of acres) to FSA at the field and subfield level. At the peak of the growing season, most county offices contract with local aerial photography companies that provide 35-mm aerial color photography of fields in slide form.

Computer programs on the System36 legacy system generate a random sample of farms that will be checked for compliance. The appropriate slides are inserted into a projector attached to a planimeter and manually rectified to the hard-copy maps. Field and subfield boundaries are measured and compared to the reported acreage.

The FSA deployed digital compliance tools. As part of the process, FSA purchased IKONOS one-meter satellite imagery from Space Imaging, Inc., for some counties. Because the photography is delivered as a rectified, digital product, service centers in these states could concentrate on compliance work in GIS without the burden of rectifying low-quality 35-mm imagery.

The next important development will be the conversion from ArcView 3.x to ArcGIS architecture. All new tools will be developed in ArcGIS. The tools available in the new environment should allow FSA to create more innovative products. The more integrated ArcGIS environment will streamline the conversion from shapefiles to database management systems.

Digitizing centers have benefited GIS literacy within the FSA. Not only have the centers become a fertile laboratory for generating ideas on migrating FSA program functions from manual processes and outdated automated technologies to GIS but center staff members also have the expertise to train employees at nearby counties and act in a help desk capacity for common problems. The contributions made by digitizing centers have been a major factor in the growth of the program and have helped deploy GIS in the centers' respective states.

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