ISLSCP II HYDRO1k  Elevation-derived Products
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File Name Description:
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There are 2 data files (*.zip) in 1 degree (1d) and half degree (hd) 
resolutions:

  1. hydro1k_elevation_1deg.zip
  2. hydro1k_elevation_hdeg.zip

When extrapolated, these files contain 26 data files pertaining to 4 elevation 
and elevation-based products and are named using the following naming convention:
hydro1k_descriptor_statistic_xd.asc, where Xd is hd (half degree) or 1d (one 
degree) spatial resolution.

In addition, 2 files at each resolution provide land/water boundary information:
hydro1k_changemap_xd.asc and hydro1k_landmask_xd.asc, where Xd is hd (half 
degree) or 1d (one degree) spatial resolution.

Please refer to 1_hydro1k_elevation_doc.pdf for further explanation of the 
file descriptions and names.

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ASCII File Format:
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All of the files in the ISLSCP Initiative II data collection are in the standard
ARCGIS ASCII GRID, or text format. The file format consists of numerical fields
of varying lenght, which are delimited by a single space and arranged in columns
and rows. The files at different spatial resolutions each contain the following
numbers of columns and rows:

 1/2 degree: 720 columns by 360 rows
 One degree: 360 columns by 180 rows

Flat areas (i.e. slope=0) are assigned the value of -1 in the median, mean and 
standard deviation in aspect files. Areas with standard deviations equal to 0 
in any parameter are undefined in both skewness and kurtosis and are assigned 
the value -99.

All files are gridded to a common equal-angle lat/long grid, where the 
coordinates of the upper left corner of the files are located at 180 degrees W,
90 degrees N and the lower right corner coordinates are located at 180 degrees 
E, 90 degrees S. Data in the map files are ordered from North to South and from 
West to East beginning at 180 degrees West and 90 degrees North. 
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