This dataset is derived from a combination of satellite imagery and national level census data using an algorithm developed by Navin Ramankutty of the University of Wisconsin. Although this image is for 1992, the dataset was originally compiled as part of a historical croplands dataset that runs from 1700 to 1990.
The grid contains fractional cropcover data, meaning the number given for each gridcell is the fraction of that gridcell's surface that is covered by crops. Thus a value of 0.7 means that 70% of the cell is being used for agricultural purposes.
Ramankutty, N., and J.A. Foley (1999). Estimating historical changes in land cover: North American croplands from 1850 to 1992. Global Ecology and Biogeography 8, 381-396.
(All images are provided at a resolution of 1600x1200 pixels)
Download a GIS grid of this data (ESRI ArcView Format)
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