Source: Landscan data 2001
Oak Ridge National Laboratory
The LandScan data set is a worldwide population
database compiled on a 30" X 30" arc second latitude/longitude
grid (roughly 1 x 1 km). Census counts (at sub-national level) were apportioned
to each grid cell based on likelihood coefficients, which are based on
proximity to roads, slope, land cover, nighttime lights, and other data
sets.
For more information see:
http://www.ornl.gov/gist/landscan/