With the density of Kwoloon Walled City (~1,255,000/km^2 in 1987 according to wikipedia), the earth's population would comfortably fit in Delaware[0]: 6.9 billion people would fit into 5498km^2, DE is 6447km^2
Worldwide, the best match would be Olt in Romania (http://goo.gl/maps/i8I02) which is precisely 5498km^2
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