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Bright Lights, Rich Cities

from ScienceNOW Daily News

Fly into a city on a clear night and you'll enjoy a jeweled panorama below. Starkly lit skyscrapers, yellow glows from the windows of scattered homes, and roads pulsing white and red as cars speed over highways and crawl along residential streets. All of this electricity usage tends to indicate that a city has money to spend. And, indeed, in a new study, economists have shown that satellite measurements of an area's lights reveal how economically developed it is.

Judging the economic status of a country like the United States is relatively easy: the relevant numbers are carefully reported and widely available, allowing anyone to easily calculate measures of economic development such as the gross domestic product (GDP). Measuring GDP isn't as easy for countries with poor financial reporting, such as many African nations, or biased reporting, as many claim China has. And economists might as well forget about documenting economic growth patterns from almost any small, remote region.

In the hope of finding an alternative means of measuring GDP, macroeconomists Xi Chen and William Nordhaus of Yale University turned to nighttime images of the globe taken by U.S. Air Force satellites. They overlaid a grid on these high-resolution images and measured the amount of light, or radiance, emanating from each cell. For countries that already provide economic information widely considered trustworthy, brighter radiance in a given region correlated tightly with a higher GDP in that region, the researchers report online in the Proceedings of the National Academy of Sciences.


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