Gridded Population of the World, Version 4 (GPWv4): Data Quality Indicators, Revision 10

The Data Context raster explains pixels with a "0" population estimate in the population count and density rasters based on information included in the census documents, such as areas that are part of a national park, areas that have no households, etc.

The Water Mask raster distinguishes between pixels that are completely water and/or ice (Total Water Pixels) and pixels that also contain land (Partial Water Pixels). The Mean Administrative Unit Area raster represents the mean input unit size in square kilometers and provides a quantitative surface that indicates the size of the input unit(s) from which population count and density rasters are created. The data files were produced as global rasters at 30 arc-second (~1 km at the equator) resolution.