code: def get_nlcd_fn():
      
      #This is original filename, which requires ~17 GB
      #nlcd_fn = os.path.join(datadir, 'nlcd_2011_landcover_2011_edition_2014_10_10/nlcd_2011_landcover_2011_edition_2014_10_10.img')
      #get_nlcd.sh now creates a compressed GTiff, which is 1.1 GB
      nlcd_fn = os.path.join(datadir, 'nlcd_2011_landcover_2011_edition_2014_10_10/nlcd_2011_landcover_2011_edition_2014_10_10.tif')
      if not os.path.exists(nlcd_fn):
          cmd = ['get_nlcd.sh',]
          #subprocess.call(cmd)
          sys.exit("Missing nlcd data source. If already downloaded, specify correct datadir. If not, run `%s` to download" % cmd[0])
      return nlcd_fn
docs: Calls external shell script `get_nlcd.sh` to fetch:
  
      2011 Land Use Land Cover (nlcd) grids, 30 m
      
      http://www.mrlc.gov/nlcd11_leg.php