From StrangeMaps :
The US is one of the worlds biggest countries, with one of the worlds most numerous populations . The 23rd Census of the United States, now under way, will provide us with updated information on the current size of Americas population, but until then, lets assume as this map does that the country is inhabited by about 300 million people. With a total area of 3,794,101 sqare miles, that gives the US a population density of approximately 79 Americans per square mile.
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Now, what if the whole population of the US would live in such a cheek-by-jowlish manner? How much space would they need? Texas? Nope. California? Think again. Pennsylvania? Nu-uh. Florida? Nice try. New Hampshire. Thats how much, or rather: how little space would be needed. The state would be ruined, though (imagine a Brooklyn-like sprawl of that size), but the rest of the country would be green and pleasantly devoid of people! As the legend to these maps point out, a further advantage would be that all Americans would be neighbors. Somehow, that does not sound like a very good idea.