Using an innovative approach with GIS and remote sensing, the Oak Ridge National Laboratory LandScanTM is the community standard for global population distribution. At approximately 1 km resolution LandScan is the finest resolution global population distribution data available and represents an ambient population (average over 24 hours).
The LandScan algorithm uses spatial data,imagery analysis technologies and a multi-variable modeling approach to disaggregate census counts within an administrative boundary. Since no single population distribution model can account for the differences in spatial data availability, quality, scale, and accuracy as well as the differences in cultural settlement practices, LandScan population distribution models are tailored to match the data conditions and geographical nature of each individual country and region.
Oak Ridge National Laboratory: http://web.ornl.gov/sci/landscan/