  Usually, the study of city population distribution has been reduced to power
laws. In such analysis, a common practice is to consider cities with more than
one hundred thousand inhabitants. Here, we argue that the distribution of
cities for all ranges of populations can be well described by using a
$q$-exponential distribution. This function, which reproduces the
Zipf-Mandelbrot law, is related to the generalized nonextensive statistical
mechanics and satisfies an anomalous decay equation.
