This directory structure was created by the R package 'Rnightlights'
available on CRAN [http://cran.r-project.org/package=Rnightlights].
It downloads satellite nightlights imagery from the NOAA, a branch of
NASA and processes them producing various statistics of any country
globally using polygon shapefiles downloaded from http://gadm.org.
The data files and other important files are stored in this directory.
The structure is as follows:

root-
    +data             directory containing the extracted country nightlight
                      data in CSV format
    +outputrasters    directory containing the clipped country rasters
    +outputrasters_webdirectory containing resampled (optional) 
                      outputrasters for faster web serving
    +polygons         the country polygons downloaded from http://gadm.org
    +temp             some temporary files (optional)
    +tiles            the satellite nightlights imagery tiles downloaded from 
                      http://noaa.usgs.gov
    +zonals           the rasters mapping raster pixels to country regions