Compare methods

	Rank-Size Rule	Spatial Gini Concentration Index
Field	Human Geography	Human Geography
Family	Process / pipeline	Process / pipeline
Year of origin	1949	1991
Originator	George Kingsley Zipf	Corrado Gini (coefficient); locational adaptation in regional science / economic geography
Type	Empirical regularity and diagnostic for the size distribution of cities	Descriptive index of how unevenly an activity is distributed across space
Seminal source	Zipf, G. K. (1949). Human Behavior and the Principle of Least Effort. Addison-Wesley, Cambridge, MA. ISBN: 9781614273790	Duncan, O. D., & Duncan, B. (1955). A methodological analysis of segregation indexes. American Sociological Review, 20(2), 210–217.
Aliases	Zipf's Law for Cities, Rank-Size Distribution, City-Size Rank-Size Relationship, Rank-Size Regularity	Locational Gini Coefficient, Spatial Gini Index, Geographic Concentration Index, Gini Index of Spatial Inequality
Related	4	4
Summary	The rank-size rule is an empirical regularity describing the size distribution of cities within a country or region. In its simplest form, popularized by George Kingsley Zipf in 1949, the population of a city is inversely proportional to its rank, so the second-largest city is about half the size of the largest, the third about a third, and so on. Generalized to a power law with an exponent q, it provides a compact way to summarize how evenly or unevenly population is spread across a settlement system and to diagnose urban primacy.	The spatial (or locational) Gini concentration index adapts the classic Gini coefficient to geography, summarizing in a single number between zero and one how unevenly an activity — an industry, a population group, a resource — is distributed across spatial units relative to a benchmark such as total population or land area. It is the workhorse measure for quantifying geographic concentration and agglomeration in economic geography.