A large human settlement, generally having extensive housing, transportation, food, sanitation, utility, land-use and communication systems. The city’s density facilitates interaction among diverse people, government organizations, institutions and businesses.
Historically, city dwellers have constituted a small proportion of humanity; however, following two centuries of unprecedented and rapid urbanization, roughly half of the world population now lives in cities and metropolitan areas, which has had profound consequences for global sustainability. Present-day cities usually form the core of larger metropolitan areas and urban areas, involving waves of daily commuters traveling into and out of city centers for employment, entertainment, education and transactions. In a world of intensifying globalization, all cities are also variously connected beyond these regions, as well as globally.
The world’s most-populated city proper is Shanghai. Meanwhile the most populous metropolitan areas are Greater Tokyo, Delhi and Jabodetabek (Jakarta).
The first known city in history was Uruk, in Akkadian Biritum/Birit Narim, or what the Greeks later called Mesopotamia, modern Iraq). Jericho (Palestine), Sidon (Lebanon), and even Eridu (Sumer/Iraq) were settled earlier, but lack the verifying documentation found at Uruk.
The first known city in the New World was Caral, Peru.
In the study of the ancient world, a city is generally defined as a large, populated urban center of commerce and administration with a system of laws and, usually, regulated means of sanitation. This is only one set of characteristics, however, and the designation of “city” can be based on such other factors as:
- Concentrated population (number of inhabitants),
- Large and/or high (multistory) buildings,
- Density of buildings/population,
- Presence of some kind of sewer system,
- Level of administrative government,
- Presence of walls and/or fortifications (by ca. 2,900 B.C.E.),
- Social heterogeneity,
- Geographical area of the settlement, or
- Whether a “settlement” was called a “city” in antiquity and meets any of the above qualifications.
The cities of Faiyum (Egypt), Damascus (Syria) and Varanasi (India) are among the cities with the longest continuous inhabitation.
 Brian Goodall, The Penguin Dictionary of Human Geography (London: Penguin, 1987); Adam Kuper and Jessica Kuper, eds., The Social Science Encyclopedia, 2nd edition (London: Routledge, 1996).
 “The demographic definition, based on the concepts of Louis Wirth, identifies cities as large, dense settlements with social heterogeneity.” Michael E. Smith, “Ancient Cities,” The Sage Encyclopedia of Urban Studies (Thousand Oaks CA: Sage Publications, 2010), p. 26.
 Nick Compton, What is the oldest city in the world? The Guardian (16 February 2015).
 Trudy Ring, Middle East and Africa: International Dictionary of Historic Places (2004), p. 204.
 Ashok Shaw, Mrinal Kanti Layek, Prerona Das, Abhijit Mukherjee, Probal Sengupta, Joy Sen, Arindam Basu, “Geological evolution of the River Ganges and its impact on the development of the city of Varanasi, India,” conference paper, Developments in Geosciences in Past Decade – Emerging Trends for the Future & Impact on Society & Annual General Meeting of the Geological Society of India, Kharagpur, October 2016.