For their dataset, the authors draw on two principle sources: “Four Thousand Years of Urban Growth: A Historical Census” (1987), by historian Tertius Chandler, which estimated the city-level populations from 2250 B.C. to 1975; and “World Cities: -3,000 to 2,000” (2003), by political scientist George Modelski, which documents the world's most important cities during three eras of history (ancient, classical, and modern). Modelski was able to extend Chandler's work by 1,475 years by using archaeological site assessments and population-density estimates.



Although both books are cited regularly by scholars, they are neither widely accessible nor easy to use since the data are not available in digital format. The new dataset, which is digitized and easily accessible, makes the historical information available for examination by other researchers, including geographers, historians, archaeologists, and ecologists



The dataset allows researchers to map and visualize city level population changes through time. For example, Istanbul, Turkey (formerly Constantinople) underwent a major period of population decline between A.D. 1057 and A.D. 1453. During this time the population dropped from approximately 300,000 to 45,000 due to a series of events including a city sacking by the Crusaders and a bout with the plague.



According to the authors, the ability to pinpoint the size and location of human populations over time will help researchers understand the evolving characteristics of the human species — particularly human interactions with the environment.



“We see this as just a starting point onto which others can add and develop into a larger record on historical population trends,” Reba said.