Simple mathematical law predicts movement in cities around the world
New research featuring a simple mathematical law shows that urban travel patterns worldwide are remarkably predictable regardless of location-an insight that could enhance models of disease spread and help to optimize city planning. Studying anonymized cell-phone data, researchers discovered what is known as an inverse square relation between the number of people in a given urban location and the distance they traveled to get there, as well as how frequently they made the trip. It accurately predicts that the number of people coming from two kilometers away five times per week will be the same as the number coming from five kilometers twice a week. The researchers' new visitation law, and a versatile model of individuals' movements within cities based on it, was reported in Nature. The researchers found that all the unique choices people make-from dropping kids at school to shopping or commuting-obey this inverse square law when considered in aggregate. "There is something really very fundamental at play here. Whether you live in Senegal or in Boston, you try to optimize your day," says study lead author Markus Schläpfer of ETH Zurich's Future Cities Laboratory in Singapore. Many researchers estimate travel with "Gravity models," which assume that movement between cities is proportional to their population sizes.