With the growing urban population, the increasing size of cities, cities have become increasingly heavy traffic loads, cities can use the public space is increasingly small.

We start at the rank-size rule by urban population and the rank-size rule by urban built-up area, and derive a mathematical relationship that the land use size of a city and its population.

With the rapid expansion of city size and population concentration, improving the urban disaster prevention system has become a daunting task can not be ignored.