New York's Grand Central Station overflows with a sea of commuters and travellers at rush hour. Every day, 1.3 million commuters travel into Manhattan to work for the day and then return to their homes at night.
A traffic jam clogs the crowded streets of Bangkok, Thailand. Urban populations around the world have boomed as economies have developed. In 1800, about 3 percent of the world’s population lived in cities; in 2000, about 47 percent lived in cities.
Cars flood the 2nd Ring Road in Beijing. The 1,763-square-mile (4,567-square-kilometre) city has been an important political and cultural headquarters for more than 2,000 years.
Taxis crowd New York City streets. Today there are about 12,000 taxis in New York, many of which drive more than 100,000 miles (161,000 km) around the city’s five boroughs every year.
A rat emerges from a New York City sewer at night. Rats are common in urban areas because they live in man-made habitats and eat human food.
Hazy golden light illuminates the Los Angeles skyline, which appears to float on a bed of smog. The city is notorious for its pervasive air pollution, caused mainly by car exhaust trapped in the San Fernando Valley basin.