In present-day China, the ongoing plan is to move 250 million people from farms into its developing megacities.
That might boggle your mind, but the most heavily populated country in the world tends to face mind-boggling issues.
Between the 1950s and 1994, tens of thousands of immigrants constructed a towering community 12 stories high across a 6.4-acre lot in Hong Kong.
It was called Kowloon Walled City.
With a population of 33,000 squeezed into the tiny lot, at its peak the city was 119 times denser than present-day New York City.
Scroll down to see the city in all its claustrophobic glory.
Though Hong Kong had been under British rule for decades by the time construction began, a clause in an 1842 treaty meant China still owned the property that would become Kowloon. Caught in legal limbo, it was effectively lawless.
By 1986, the Walled City had caught the attention of photographer Greg Girard. Girard would spend the next four years in and out of the city, capturing daily life inside its teetering walls.
The Lego-like city was built over decades, as residents simply stacked rooms one on top of another. The end result "looked formidable," Girard says, "but who knows?"
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