This week, we're asking what it really means to live in a world with 7 billion people. For some answers, we visit Karachi, Pakistan.
The grandest expression of the world's population growth is in the word "megacity." Dozens of these cities of more than 10 million now ring the globe, like a string of oversized pearls. In a megacity, people and ideas clash: The ancient collides with the modern; secular with religious; global with local. In Karachi, Pakistan, those forces can be seen in the story of a single piece of real estate.