- They start with the DISCover land cover dataset, which classifies each of the 1 x 1 km cells into one of several land use types, based on monthly NDVI data from March of 1992 through February of 1993.
- These classifications are then regrouped into six categories: (0) other vegetation, (1) other vegetation with crops, (2) other vegetation/crop mosaic, (3) crop/other vegetation mosaic, (4) crops with other vegetation, and (5) crops.
- The fraction of a cell used for agriculture is calibrated for each of these six labels, to match with the national-level total cropland area from FAOSTAT and other sources.
- The 1 x 1 km cells are aggregated into the 5 x 5 arc-minute cells.
Ramankutty and Foley (1999) update this dataset by using alternative data sources etc., as part of their "Historic Croplands Dataset, 1700-1992."