A city is a large human settlement. Cities generally have extensive systems for housing, transportation, sanitation, utilities, land use, and communication. Their density facilitates interaction between people, government organizations and businesses, sometimes benefiting different parties in the process.
Historically, city-dwellers have been a small proportion of humanity overall, but following two centuries of unprecedented and rapid urbanization, roughly half of the world population now lives in cities, which has had profound consequences for global sustainability. Present-day cities usually form the core of larger metropolitan areas and urban areascreating numerous commuters traveling towards city centers for employment, entertainment, and edification.
