What if everyone lived in one city
As of March 2016, the number of humans alive in the world is at $7.4 billion people. But what if every single last one of us, everybody watching this video, including you, all lived together in the same city? How big or small would this city look like? And how close together would we all have to live? Let's pause and think for a moment about where we all currently live. 60% of us live in Asia, while 16% live in Africa, 10% in Europe, 8% in North America, 5.5% in South America, just 0.5% in Australia and Oceania, and too little people to even register on the scale in Antarctica. So first off, we would have to agree on which continent, or island, we would migrate everybody in the world to. 50.5% of everybody in the world currently lives in a city, so we would have to convince the other 49.5% of people to come and join us. So now assuming that we have gathered everybody together in the same place to create our city, let's look at some real life examples to see what living so close together might actually look like. Singapore is the most densely populated country in the world right now. Five million 399,000 people live in the small country of just 710 square kilometers. That means that, for every square kilometer in size within the country, there are 7,605 people living out their lives on average. But Singapore is a country the size of a city, and there are much more densely populated cities than that already in the world. For reference, downtown Manhattan in New York City has a population density of 26,939 people every square kilometer. That's a lot of people very close together, but we're just scratching the surface. The densest city in the world right now is Manila, in the Philippines, where you will find 41,515 people every square kilometer. But Manila's total population is relatively low, at just 1,780,000 people. The density of people is just so high because they all live together in such a small space. The biggest concentration of people in one place anywhere in the world can be found here in Japan, the Tokyo metro area, home to 36,923,000 people. To put into perspective just how enormous Tokyo is, I'm going to show you two examples to illustrate the point. First, this is an image of the United Kingdom with the area of the greater London metro highlighted in red. And if you think that looks big, this is the greater Tokyo metro area highlighted in blue. It's truly gargantuan. But onto the second example. This is an image taken of downtown Tokyo. But if we zoomed out further to here, then the exact location of downtown grows much harder to find. Let's trade out this photo for a new one, which shows the true size of Tokyo as seen from the sky. In this one photo that you're looking at, lives nearly the same population as all of Australia, New Zealand, and Oceania combined, or about 0.5% of everybody in the world, all in one city. But we still have the other 95.5% of the human population to think about. And we can still fit people into a much smaller space. Right now, in 2016, the highest concentration of people living in a smaller place than a city is probably within the city of Mumbai, India. Located within the city is a slum called Dharavi, which is an area just 2.17 square kilometers in size. If we think about that size and compare it to Central Park in New York City, the Dharavi slum would only take up 64% of the same size, or not even 2/3 of the area. And living in that cramped tiny space or anywhere between 700,000 to 1 million people. Averaging out those numbers, we get 391,705 people every square kilometer. Now this number here is the highest number of people in the world today that live in a square kilometer. As recently as the 1980s, however, there was a place that was somehow even more frighteningly claustrophobic. The most densely populated place known in history was the Kowloon Walled City, which was located here in Hong Kong. To get some kind of idea of what we're going to be talking about, this image is an aerial view of the city from 1987. You can kind of get some scale of it by looking at the basketball courts over here on the right, or the trucks over here on the left. But the overall total area of these buildings is just 0.26 square kilometers. Another way to possibly imagine how tiny that really is is this way. Here are three American football fields side by side. The Kowloon Walled City would be just a little bigger than them put together. And 33,000 people were living in that tiny space. Meaning that, if we stretched that out to a full square kilometer, the population density would be 1.2 million people. Living that close together would look something like this image, and this number is the absolute limit that we've ever seen in the real world of how many people can live together in such a small area. So now let's visualize how big our hypothetical global city would have to be according to the different population densities that we have been discussing. First, let's imagine something a little comfortable. Let's take the city of New Orleans in Louisiana, whose population density is about 784 people per square kilometer. On that scale our global city would be about the same size as roughly the continental United States. If we moved onto the density of say, Austin, Texas, we would be looking at a city that is about the size of Australia, with room left to spare. But we want to get even smaller than that. So we're going to try fitting everybody into the same density as Chicago next. On that scale, our city would be about the same size as Iran. But let's get even smaller. At the density of Singapore, we could fit the entire human race into just the states of Texas, Oklahoma, and Louisiana-- already considerably smaller than at the New Orleans density. But we're going to keep on getting even smaller. At the density of Manhattan, we would be looking at a city about the size of Ecuador, here in South America. And if we had a city with the same density we see in Manila, then everybody in the world would fit inside the US state of Missouri. But to get even more frightening and claustrophobic our global city with the same density seen within the Dharavi slum in Mumbai would be about the same size as New Jersey. And finally, at about the absolute real world limit, if we built our global city with the same population density as Kowloon Walled City, we would fit every single person in the world into an area about the same size as Palestine, which itself is only about half the size of the Tokyo metro area. Let's put all of these different sizes in a row to get possibly the best visualization. First, we have a city with the same density of New Orleans, followed by Austin, Chicago, Singapore, Manhattan, Manila, the Dharavi slum, and finally the Kowloon Walled City. Whichever way you look at it, living together in the same city would be both bizarre and leave an enormous amount of empty space left in the world.
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