Professor of Planning School of Planning
University College London, United Kingdom

There is an urgent need for a new taxonomy of cities to take account of developments observable in the last two decades:

1. Increasing competition between cities for the highest-level informational services, most evident in the European Union, but also observable in the United States and Pacific Asia;

2. The growth of "million cities" in the developing world, some of which may compete for global city status early in the 21st century;

3. Decentralization of people and activities from some of the largest global cities (London, New York) into extended polycentric city regions;

4. Even more extended decentralization from some cities in Pacific Asia, leading to the formation of Mega-Cities (Pearl River Delta, Greater Jakarta);

5. The phenomenon of "hypertrophic" urbanization in sub-Saharan African cities, where growth occurs without an evident economic base.

The paper will discuss these trends and will attempt to propose a new taxonomy for cities at the top of the global urban hierarchy.