Have you ever heard about a mysterious law that predicts the size of a city? If you tell me the population of the largest city in a country, I can tell you the size of the second and third biggest cities. In 1949, George Zipf came up with the simple theory called the rank-size rule, or “Zipf 's law.” Applied to the size of cities, this law says that the second city and following smaller cities should represent a proportion of the largest city. For example, if the largest city in a country is populated with one million citizens, according to the law, the ...