ABSTRACT
According to different definitions, megacities are on a purely quantitative level those metropolises with a population of over 5 million (Bronger 1996a, 1996b), more than 8 million (UN 1987, p. iii; Fuchs et al. 1994, p. 1, 42, 43; Chen & Heligman 1994) or more than 10 million inhabitants (Mertins 1992). Some authors also set a minimum level for population density (at least 2,000 persons/km2) and only include cities with a single dominant centre (Bronger 1996a, 1996b), whereby polycentric agglomerations such as the Rhein-Ruhr area in Germany, for example, with 12.8 million inhabitants, are excluded. Others include this polycentric mega-urban region (UN 2002, p. 116 ff.). Ultimately it is futile to fight over a fixed definition of megacities, as any setting of minimum/maximum values is subjective and thus open to debate. Furthermore, there are the problems of inconsistent spatial boundaries for administrative districts, as well as the reliability of up-to-date population figures given inconsistent censuses, projections and estimations. International statistics are not based on similar areas of reference, so that the figures given for the size of cities and megacities are generally not comparable.
