A TALE OF FIVE CITIES AND HOW THEY GREW

BY CLARE TRAINOR, JASON TREAT, AND KELSEY NOWAKOWSKI

Rail, roads, and real estate play a role in the physical shape of cities. So does geography. To track how metropolitan regions have developed, Shlomo Angel and his colleagues at New York University used historical maps and satellite imagery to create the Atlas of Urban Expansion. The atlas defines city parameters to include the entire built area beyond a city’s jurisdictional boundaries and into surrounding municipalities.

INNOVATIONS THAT SHAPED CITIES

RESISTING ATTACK

Walls long protected cities from invaders. Cannons became a threat—until residents developed thick, sloped walls able to withstand blasts. Once nation-states made the walls unnecessary, cities could spread out.

FACILITATING TRADE

Port cities flourished as global centers of industry. To move cargo inland, rail lines extended out from the cities into the country in all directions. This led to tentacle-shaped development patterns.

MOVING PEOPLE

When the elevator was introduced in the 1850s, cities grew denser and taller. Cities were able to stretch farther into the suburbs when cars and buses filled in the transportation gaps left by rail lines.

LOS ANGELES, UNITED STATES

Real estate developer Henry Huntington bought up land on the outskirts of Los Angeles in the late 1890s. Then he established the Pacific Electric Railway to link the scattered suburbs. The interurban rail system, which operated from 1901 to 1961, propelled the city’s expansion and for a time was the world’s largest electric-powered system. Eventually it was dismantled and replaced by bus lines and cars, making sprawl the norm.

Urban extent by year

2000

2014

1890

1920

1950

1980

1990