Put more simply, this implies that the largest city is twice as large as the second-largest city, three times as large as the third and so on along the uiban hierarchy. While the relationship tends to break down at small scales, it holds remarkably well for many countries across a very wide range of city sizes (Gabaix and Ioannides, 2004). There is also the question of whether Zipfs Law implies some constraints in the pattern of uiban growth, i.e. that the growth trajectories of individual cities could not change the overall city-size distribution (Duranton, 2007).