View the map at http://ryanhamley.github.io/historic-urban-population-timeline/dist/
Reba, M. L., F. Reitsma, and K. C. Seto. 2018. Historical Urban Population: 3700 BC - AD 2000. Palisades, NY: NASA Socioeconomic Data and Applications Center (SEDAC). https://doi.org/10.7927/H4ZG6QBX. Accessed August 15, 2018
Reba, M. L., F. Reitsma, and K. C. Seto. 2016. Spatializing 6,000 Years of Global Urbanization from 3700 BC to AD 2000. Scientific Data 3: 160034. https://doi.org/10.1038/sdata.2016.34.