India's largest city is also one of the largest cities in the world, both in size and population. Nearly 20 million are crammed into an area of 1,600 square mi—that's about 11,000 people per square mi. On a peninsula jutting out of the western coast of India and facing the Arabian Sea, in the state of Maharashtra, Mumbai is roughly equidistant from the three other main Indian cities of New Delhi, Kolkata, and Chennai.