The LandScan 2001 global population data set is a worldwide population database compiled on a 30" X 30" latitude/longitude grid. 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. LandScan has been developed as part of the Oak Ridge National Laboratory (ORNL) Global Population Project for estimating ambient populations at risk. The LandScan files are available via the internet in ESRI grid format by continent and for the world. At approximately 1 km resolution (30" X 30"), There is also a "Layer" file (lspop2001.lyr) for ArcGIS. LandScan is the finest resolution global population distribution data available and represents an ambient population (average over 24 hours). This dataset is part of the LandScan 2000 Global Population Database (2000-2010). Developed for the U. S. Department of Defense. Allows for quick and easy assessment, estimation, and visualization of populations-at-risk. "Since natural or man made emergencies may occur at any time of the day, the goal of the LandScan model is to develop a population distribution surface in totality, not just the locations of where people sleep. Because of this ambient nature, care should be taken with direct comparisons of LandScan data with other population distribution surfaces." --from the Oak Ridge National Laboratory LandScan Web site, Sept. 12, 2013. Oak Ridge National Laboratory. (2002). LandScan 2001 Global Population Database. Oak Ridge National Laboratory, UT-Battelle, LLC. Available at: http://purl.stanford.edu/zv809qg5890 IMPORTANT: For correct population analysis using ESRI products assure that the following parameters are set: -Use ONLY Geographic, WGS84 projection parameters. -Spatial Analysis cell size is 0.008333333333333 (double precision) -Spatial Analysis extent should be set to an exact multiple of the cell size (for example 35.25, 35.50, 35.0) Converting (including on-the-fly projections) a grid to other projections or coordinate systems causes population cells to be re-sampled, and hence population counts will be incorrect. In ESRI ArcMap, load the LandScan grid first in order to maintain the original geographic (lat-lon) projection.