Urban agriculture is clearly taking off around the world — in backyards, on rooftops and on local farms.

But just how much of the world’s cropland can we really call urban? That’s been a big mystery.

Now, a study published in the journal Environmental Research Letters has an answer: Somewhere around 1.1 billion acres is being cultivated for food in or within about 12 miles (20 kilometers) of cities. Most of that land is on the periphery of cities, but 16.6 percent of these urban farms are in open spaces within the municipal core.

The researchers — who hail from the International Water Management Institute, the University of California-Berkeley and Stanford University — looked at a combination of remote-sensing analyses of satellite imagery and agricultural census, population and socioeconomic data. They say theirs is the first global assessment of urban croplands and the water they consume.

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