  An Atlas model is a rank-based system of continuous semimartingales for which
the steady-state values of the processes follow a power law, or Pareto
distribution. For a power law, the log-log plot of these steady-state values
versus rank is a straight line. Zipf's law is a power law for which the slope
of this line is -1. In this note, rank-based conditions are found under which
an Atlas model will follow Zipf's law. An advantage of this rank-based approach
is that it provides information about the dynamics of systems that result in
Zipf's law.
