Are mega-cities wrecking urban hierarchies? A cross-national study on the evolution of city-size distribution

The increasing number of mega-cities and their dramatic growth accompanied by the prevailing urbanization processes raise concerns about the polarization of urban hierarchies. For a long time, policy makers have sought to reduce polarization through spatially targeted interventions. Yet, the academic basis for these interventions is insufficient, especially for policies based on cities of different size. Using a data set covering the 1950–2018 period and fixed-effect models, this paper explores the trends in city-size distributions at the national level and the key determinants at both national and city level that shape city-size distributions and city growth. The results show that: 1) city-size distribution worldwide has remained generally unchanged over the last seven decades; 2) national urbanization supports smaller cities and thus prevents the polarization of urban hierarchies; and 3) the opposing effects of different factors on city-size distribution and the growth of cities of different sizes cancel each other out, underlying the stability of urban hierarchies. Thus, we argue that currently there is little ground to worry about skewed urban hierarchies.