This README file describes the contents of each gzipped, tarred folder.

You can obtain the 1992 global croplands data set at two different resolutions:
a) 0.5 deg resolution in latitude x longitude - get the file 'crop92_0.5.tar.gz'
b) 5min resolution in latitude x longitude - get the file 'crop92_5min.tar.gz'

Each of these gzipped, tarred folders contains the following files.
1) README - a copy of this file.
2) crop92_v1.1_5min.nc - the global croplands data set described in Ramankutty 
and Foley (1998), updated to a newer version. File format = NetCDF.
OR crop92_v1.1_0.5.nc - same as above, but aggregated to a 0.5 deg resolution.
3) readnc.f - a FORTRAN program to read the NetCDF files.
4) ies-io.f - a FORTRAN program that contains NetCDF subroutines.
5) makefile - a makefile to compile the programs used to read the NetCDF files.

Version updates:

Version 1.0:
In Ramankutty and Foley (1998), a 1 km resolution satellite-derived land cover
classification data set, DISCover, was calibrated against a suite of national
and subnational cropland inventory data to create a 5 min resolution (approx.
10 km on a side) data set of fractional croplands in each grid cell. 

Version 1.1:
We updated the cropland inventory data set and recalibrated the DISCover data 
against it. The inventory data were updated in the following ways:
1) We used adjusted FAO cropland inventory data from Alexandratos (1995) 
for 91 developing countries. But we later realized that the adjustments 
were questionable for some countries such as Brazil. Hence, in version 1.0, 
we decided to use the original FAO data.
2) We corrected some of the data for Yugoslavia - the old version had some
minor errors made while splitting the total for the Federal Republic of 
Yugoslavia into the currently existing countries.

The recalibration yielded the following result:

Table. 2 from Ramankutty & Foley (1998), but updated to version 1.1
-----------------------------------------------------------------------------
	Other  Other  Other  Crop/   Crops  Crops   Correl.  Slope  Intercept
	 veg	veg   veg/   other    with  
	       with   crop    veg     other
	       crops  mosaic  mosaic   veg
-----------------------------------------------------------------------------
N.Amer   0.0    0.3    0.7    0.7     0.85   1.0     0.936   1.085    303.26
S.Amer   0.0    0.1    0.1    0.25    0.45   1.0     0.716   0.933    768.09
Africa   0.0    0.05   0.5    0.5     1.0    1.0     0.788   0.920    399.97
Eurasia  0.0    0.15   0.15   0.5     1.0    1.0     0.934   1.100    939.62
Aus.Pac  0.0    0.15   0.6    0.6     0.6    1.0     0.963   1.083   -805.73
-----------------------------------------------------------------------------

v1.1 differs from v1.0 in the following ways:
1) crop areas significantly decreased in South America,
2) crop areas decreased slightly in Africa,
3) crop areas increased slightly in North America, Eurasia & Australia-Pacific.
 
Ramankutty, N. and J. Foley, 1998: Characterizing patterns of global land use:
An analysis of global croplands data, Global Biogeochemical Cycles, 12, 667-685.

For any questions, contact:
Navin Ramankutty
nramanku@students.wisc.edu