The Global Rural-Urban Mapping Project, Version 1 (GRUMPv1) consists of estimates of human population for the years 1990, 1995, and 2000 by 30 arc-second (1km) grid. The area
grids measure land areas in square kilometers and the mean unit size (population-weighted) in square kilometers. The land area grid permits the summation of areas (net of permanent ice and
water) at the same resolution as ... the population density, count, and urban-rural grids. The mean unit size grids provide a quantitative surface that indicates the size of the input unit(s)
from which population count and density grids are derived. Additional global grids are created from the 30 arc-second grid at 1/4, 1/2, and 1 degree resolutions. This dataset is produced by
the Columbia University Center for International Earth Science Information Network (CIESIN) in collaboration with the International Food Policy Research Institute (IFPRI), The World Bank,
and Centro Internacional de Agricultura Tropical (CIAT).