The United States Department of Agriculture (USDA), National
Agricultural Statistics Service (NASS) area sampling frame is a
delineation of all parcels of land for the purpose of later sampling the
parcels. The area frame is constructed by visually interpreting satellite
imagery to divide a state into homogenous land use areas (strata) based
on percent cultivated. The strata are typically defined as low, medium or
high percent cultivated, non-agricultural land, urban use, agri-urban, or
water. The boundaries of the strata usually follow identifiable features
such as roads, railroads and waterways. The strata boundaries do not
coincide with any political boundaries, with the exception of state
boundaries.
Though all of the dates for this frame point to 2005, this is only when the
older frame from the paper map was converted over to digital form. All of
the stratification work for the paper maps and was completed in 1984.