Read more about this map at http://www.jakelow.com/essays/mapping-the-world-population
This gist includes coarse data derived from SEDAC's UN-adjusted population density grids. The original data has a resolution of about 2.5 arc minutes. It's distributed as a 43200x17400 GeoTIFF file. In order to produce coarser data, I ran the following command:
gdalwarp -t_srs EPSG:4326 -tr 0.5 0.5 -r average gpwv4-unpd.original.tiff gpwv4-unpd.very-coarse.tiff
If you want to use higher-resolution data than is provided in this Gist, download the original dataset from SEDAC and run the same command, but substitute smaller values, e.g. -tr 0.1 0.1
.