File Name Convention
--------------------
The files in this data set are named "historic_cropland_XX_YYYY.asc", where XX can be 
either hd or 1d, meaning a spatial resolution of 0.5 and 1 degree in both 
latitude and longitude, respectively and YYYY is the year from 1700 to 1992. For 
each spatial resolution, 24 files with global croplands fraction cover from 0 to 
1 are provided for every 50 years from 1700 to 1850, every 10 years from 1850 to 
1980, and every year from 1986 to 1992. An additional file called 
"historic_cropland_hd_chngmp.asc" is also provided that shows the differences between 
the original land/water mask and the land/water mask used in this collection. 
Note that the land/water mask difference file is only available at a 0.5 degree 
spatial resolution.

##############################################################################

ASCII File Format
------------------
All of the files in the ISLSCP Initiative II data collection are in the ASCII, 
or text format. The file format consists of numerical fields of varying length, 
which are delimited by a single space and arranged in columns and rows. The 
files in this data set contain 720 columns by 360 rows for the 0.5 degree data 
sets, and 360 columns and 180 rows for the 1 degree data sets. All values are 
written as real numbers. Water bodies are assigned the value of -9.999 while 
land areas with no data are assigned the value of -8.888. 

The values in the "historic_cropland_hd_chngmp.asc" file represent the differences 
between the 0.5 degree ISLSCP II land/water mask and the original land/water mask 
and mean the following:
 -1 = ISLSCP II mask is water and original data is land (data removed)
  0 = Data sets agree over land or water (data unchanged)
  1 = ISLSCP II mask is land or water and original data is missing (fill value used).

the files are gridded to a common equal-angle lat/long grid with spatial
resolutions of 0.5 X 0.5 degrees and 1.0 X 1.0 degrees in latitude and 
longitude, where the coordinates of the upper left corner of the files are 
located and 180 degrees W, 90 degrees N, and the lower right corner
coordinates are located at 180 degrees E, and 90 degrees S.