I made this map using the GDAL module for Python. First, I wrote a script that created a shapefile grid for the world, with each square cell representing a 10 degree by 10 degree area. Then, I wrote a script that intersected this grid with a shapefile map of the world that had a GCS_84 coordinate system. Based on this intersection, the script created a new shapefile which contained information on what percentage of each grid contained dry land. Finally, I opened the shapefile in ArcMap and assigned symbol levels. My code and land cover data can be found here.