Where’s Waldo . . . and 6 billion others?

Scientists at Oak Ridge (Tenn.) National Laboratory have combined satellite imagery and detailed census data to develop a worldwide database that can provide estimates of the number of people located in areas on a grid that has boxes with areas of 1 square kilometer or less.

The researchers describe the LandScan database, which they say will help determine populations at risk from natural and manmade disasters, in the July Photogrammetric Engineering & Remote Sensing.

Jerome E. Dobson and his colleagues used satellite images and other geographic data to determine land characteristics, such as the slope of terrain, and the prevalence of roads and nighttime lights.

With this information, scientists can estimate the number of people located in rectangles measuring 30 arcseconds of the Earth’s circumference on a side. Such cells measure 1 km on a side at the equator and become smaller as latitudes increase.

Although future versions will provide both a daytime and a nighttime allocation of people, the new database gives a single estimate. For example, the calculations assume that the traffic on roads stretching through unpopulated deserts will place small numbers of people in the area during the day.

“This database has a higher resolution and is more realistic than any that’s been produced to date,” says Andrew T. Bower, a geospatial analyst at the National Imagery and Mapping Agency in Washington, D.C.

The researchers are currently working on next year’s model. “We recently received a ton of data—literally,” Dobson says. The two pallets of CD-ROMs, which weighed a total of 2,086 pounds, contained geographical information that’s far more detailed than what’s included in the current model.

Dobson predicts that government agencies will use the high-resolution population plots to estimate numbers of people at risk from volcanic eruptions, floods, and other large disasters, as well as from more localized threats, such as releases of toxic chemicals. Personnel at the State Department have already taken advantage of the LandScan model—when they planned the U.S. response to the flooding in Mozambique last March.

“The better an idea we have of where people are and how they can be reached, the better they can be helped,” says William B. Wood, director of the State Department’s Office of the Geographer and Global Issues.

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