Here's what life is like in the world's most crowded cities

Mohammad Ponir Hossain/Reuters

A man in Dhaka, Bangladesh leaps between the crowded train cars.

Urbanization is taking over the world.

By the year 2050, 70% of the world will live in cities, according to the Population Reference Bureau.

One of the most striking ways to see this growth is through the lens of population density, or the statistical measure of a city's congestion.

The most population-dense cities grapple with unique challenges. They fight for resources, like housing and personal space, and they put infrastructure to the test.

Here's just a taste of what life is like.