## The dynamic of the geographical distribution of a population

Gustavo De Santis, *University of Florence*

Giambattista Salinari, *University of Florence*

The frequency distribution by population size of a set of geographical areas approaches a log-normal curve: we develop a theoretical framework to explain why this happens, and the reason is that a markovian process is in place. The population at time t+1 of each unit can be thought of as determined by the population of the same unit at time t plus a random component, distributed as a normal variable, whose parameters (mean and variance) depend on the population size of the unit at time t. In particular, the units with a larger starting population are characterized by a greater variance in their subsequent evolution. The model applies satisfactorily to the geographical distribution of virtually all European populations in several years, and using different units of analysis

Presented in Poster Session 3: Migration, environment and spatial demography