The frequency with which the settlements of a country or region occur in certain, arbitrarily defined, population size groups. Generally, large settlements are less frequent than small ones, but when size is graphed against frequency, several patterns may be recognized. Iyer (2003) Eurasian Geog. & Econ. 44, 5 documents the change from a relatively uniform city-size distribution ‘in accordance to Marxist ideals’ to increasing evenness in post-Soviet Russia. See Overman and Ioannides (2001) J. Urb. Econ. 49, 3.