How lights define a city

And other recent highlights from the Ideas blog

The United States at night is seen in this composite image.


The United States at night is seen in this composite image.

You’ve likely seen nighttime satellite pictures of Earth before—images that show Tokyo and New York blazing away and a swath of darkness over the ­Sahara.

These images offer a vivid picture of human activity around the world, and now it turns out they may be instrumental in solving a practical problem in the social sciences: how to define where metropolitan boundaries begin and end.


Currently social scientists lack a consistent way of doing that, which makes comparisons across studies and among metro regions difficult. But a paper published earlier this year in The Professional Geographer suggests that light measurements from nighttime satellite images can be used to define metropolitan boundaries consistently in cities around the world.

As you’d expect, light intensity is highest in city centers and diminishes as you move outward. The authors, led by the prolific Richard Florida of the University of Toronto, had to make a judgment call about the light threshold that marks the end of a metro region. But the beauty of their method is that once the light threshold is set, it gives you a consistent measure of metropolitan size. (More consistent, for example, than metrics like commuting time, which don’t translate well from city to city.)

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Having gathered light data, the authors then use it to estimate economic activity: They multiply national gross domestic product by the share of light emissions coming from a given metro area, and arrive at a measure they call “light-based regional product.” From this, the authors conclude that the 10 largest metropolitan areas in the world—which contain only 2.6 percent of the world’s population—account for 21.2 percent of global economic activity.

Half the fun of the article is poring over its rankings of metro areas. Tokyo-Kawasaki-Yokohama is the brightest—and richest—in the world, with an economic output of $1.9 trillion, nearly twice the output of the New York-Philadelphia-Newark corridor, which comes in at number two.


The skateboard in the “Firefly” video is ringed with blue LED lights, and traverses an unnamed city.

Drones are everywhere these days. They’re in Pakistan, of course, and recently in Brainiac I wrote about how unarmed airplanes are being deployed in South Africa to combat rhino poachers. Now comes a beautiful example of what you might call drone-enabled art—“Firefly,” a skateboard video, of all things, shot from a remote-controlled helicopter and produced by the Czech company Samadhi Production.


The skate video takes place in an empty, unnamed city at night (if you recognize any landmarks, let us know) and the board is ringed with blue LED lights that create an ethereal glow around the skateboarder as he glides through expressway tunnels and jumps down stone staircases. This, combined with the unique aerial perspective plus a heavy does of electro-orchestral music, creates a vaguely ominous but also strangely moving viewing experience.

For more drone-enabled art, check out Richard Jackson’s “Accidents in Abstract Painting” from earlier this year, where a paint-filled drone crashes into a wall.

Kevin Hartnett is a writer who lives in Ann Arbor, Mich.
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