Unit of observations: 30 arc-second grid
The dataset measures person-hours so that the presence of people in commercial areas during daytime is not undercounted.
Person-hour estimates are derived from census counts and satellite images of geography. Thus, census population data is interpolated spatially.
Only the 2006 data is available for newly registered users (as of February 2008).
Used by Nunn and Puga (2007) to calculate the correlation between population density and terrain ruggedness for each country.
Data for 2000 was used by Alesina et al. (2013) to estimate population of each language group across the world.