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Best estimates indicate that Earth is now home to 6 billion people, half of whom live virtually on top of each other in rapidly growing urban areas. The consequences of this burgeoning human population impact everything from climate change and world hunger, to pollution, geologic hazards, biodiversity loss and more.
Yet, despite the relevance of population to social and environmental research and problem solving, reliable data has been difficult to come by. Errors and inconsistencies between the census methods of different governments make cross-border comparisons difficult, while data based on arbitrary geopolitical boundaries often do not coincide with researchers' needs.
To address this problem, Columbia University's Center for International Earth Science Information Network (CIESIN) has produced the Gridded Population of the World (GPW), a multifaceted database now available as an on-line web service. Designed to facilitate the use of population data in interdisciplinary research, GPW offers the best-available census information in a format free from the constraints and complications of administrative borders.
"The real beauty of this product is that researchers will be able to draw population distribution and density data into their work without the usual struggle and uncertainty," said Deborah Balk, senior research associate at CIESIN and GPW project leader within its NASA-funded Socioeconomic Data and Applications Center (SEDAC). "It's a huge undertaking to handle raw population data. In making this database publicly available, we hope to free other researchers from that tedious effort so that they can focus on the real work of data interpretation."
A preliminary beta version of the web site was released Tuesday, April 25th for use and comment within the Columbia community. It can be accessed at http://sedac.ciesin.org/plue/gpw/. A wider release of the site is planned for late May or early June.
In creating GPW, Balk and her colleagues gathered and synthesized census data from more than 125,000 administrative units around world, producing fully integrated best estimates for the distribution of global population in 1990 and 1995. The resulting data set was then superimposed onto a latitude-longitude grid of almost 8 million cells representing Earth's land surface.
Using GPW will enable researchers to quickly and directly compare population data with other "geo-referenced" information such as physiography and roads, agriculture and land-use patterns, geologic hazards, and climate and pollution data. The GPW will be particularly useful in comparing population data with the new generation of satellite imagery now becoming available.
Color-coded maps of the world and individual continents that show both population density and change from 1990 to 1995 are accessible on GPW and can be downloaded. The underlying data, methodology and documentation can also be accessed right down to the individual grid cells, which represent just a few square miles of land on average.
"At CIESIN alone, my colleagues and I are currently using GPW in research projects ranging from environmental sustainability to climate-health interactions, wetlands protection and natural hazards vulnerability," Balk said.
The new GPW release actually represents the product's second iteration. Since the original was launched on-line in 1995 by the National Center for Geographic Information and Analysis in collaboration with CIESIN, researchers from across the spectrum of earth science, biology, agriculture, health science and economics have referenced it in peer-reviewed publications. And with the many improvements of the new version better raw census data normalized by country to match United Nations estimates, four times the grid resolution and a more accurate population allocation algorithm Balk hopes to see use soar.
Lamont-Doherty Earth Observatory research scientist Christopher Small, who has a paper in-press with Vivian Gornitz of the Columbia's Center for Climate Systems Research and Joel Cohen, director of The Rockefeller University's Laboratory of Populations, has used both versions and sees the increased utility.
"The original version enabled us for the first time to investigate in a quantitative, systematic manner the relationship between the global distribution of human population with climate and landscape," Small said. "The new GPW provides substantially more resolution, particularly in the many densely populated parts of the world that are hardest to resolve."
"For example, it now appears that half the world's human population lives on less than 3 percent of the ice-free land," Small said. "The implications of that fact alone are enormous."
And although researchers form the primary audience, the interactive graphical character of GPW renders it ideal for both in-class and at-home educational use, Balk said.
Despite the advances though, GPW remains a work-in-progress. Beyond eventually incorporating new census data for 2000, other planned refinements already on the table include adding layers of demographic complexity such as population age distribution, income/poverty levels, human settlements and urban areas, land use, nutrition level and source, energy use and overall resource consumption. And the active participation of GPW users in its incremental improvement is warmly welcomed, Balk said.
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