As most of us know, a great deal of our food travels long distances by planes, trains, trucks and ships before reaching our dinner plates.

Even California – the fruit, nut and vegetable bowl of the United States – imports some of its asparagus from Peru, table grapes from Chile, Navel oranges from Australia, and tomatoes from the Netherlands.

With more than half the world’s population now living in cities, getting food to where the people are – and getting water to the farmers who grow that food – is an increasingly big challenge.

Yet a surprisingly large share of the world’s cropland is found not in rural areas, but within cities and their immediate surroundings. Some 456 million hectares (1.13 billion acres) of land is cultivated directly in cities or within 20 kilometers (12.4 miles) of an urban perimeter, according to a recent study conducted by researchers at the International Water Management Institute in Colombo, Sri Lanka, the University of California-Berkeley and Stanford University, and published in the journal Environmental Research Letters.

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