City

A city is a human settlement of substantial size.

While the term varies globally, it often describes a permanent, densely populated area. These places have administratively defined boundaries. Most residents in a city work on non-agricultural tasks. Cities rely on extensive systems for housing, transportation, and sanitation. They also manage utilities, land use, and communication. This high density facilitates interaction between people, businesses, and governments. This interaction can improve the efficiency of distributing goods and services.

Defining a city can be complex because there is no universal size limit. Some definitions for urban areas range from 1,500 to 50,000 people. In many U.S. states, a minimum of 1,500 to 5,000 inhabitants is required. National censuses use many factors to classify populations as urban. These include population density, the number of dwellings, and economic functions. A modern metric endorsed by the United Nations requires at least 50,000 inhabitants in contiguous dense grid cells. These cells must have more than 1,500 inhabitants per square kilometer.

Beyond size, cities serve specific functional roles. They act as administrative, commercial, religious, and cultural hubs. A city often has a special symbolic status granted by a central authority. For example, in the United Kingdom, city status is awarded by the Crown. This can result in very small cities, such as St Davids. Cities often feature a literate elite due to cultural diversity. They typically include professional administrators and systems of taxation. This structure differs from the informal agreements found in tribes or villages. Such organized societies are often called civilizations.

Geography plays a massive role in where cities are located. Historically, access to water has been a major factor for growth. Most urban populations live near a coast or a river.

This is because cities generally cannot produce their own food. They must maintain a relationship with a hinterland that sustains them. Most cities are central to a productive region. They serve as marketplaces in locations that are easy to reach. Some exceptions exist, such as mining towns that rely on long-distance trade.

Cities possess distinct internal structures and patterns. These patterns are often shaped by the physical environment. A geomorphic structure follows the natural land, like terraces on a mountainside. Other patterns include radial, concentric, rectilinear, and curvilinear designs. In a radial structure, main roads converge on a central point.

Dutch cities like Amsterdam use concentric canals to mark expansion. A rectilinear pattern uses a grid plan of straight streets. The Indus Valley Civilization used this for cities like Mohenjo-Daro.

This grid system is also seen in the ancient Greek city of Priene.

Urban life has changed significantly throughout human history. Cities have existed for thousands of years. Archaeologists identify Jericho and Çatalhöyük as early proto-cities from the eighth millennium BC. The Mesopotamian city of Uruk was a major center in the mid-fourth millennium BC. Traditionally, cities followed the development of agriculture. Surplus food allowed for a social division of labor. However, some believe cities arose from fishing or military needs instead. Ancient leaders, including Alexander the Great, were known for founding new cities.

Today, the scale of urban life has profound global consequences. More than half of the world's population now lives in cities. This rapid urbanization impacts global sustainability and climate change. Cities often form the core of much larger metropolitan areas. These areas include suburbs and exurbs used by commuters. Some regions even form a continuous landscape called a megalopolis.

Dense, compact cities can have a smaller ecological footprint per person. They use less land and offer efficient transportation.

However, high concentration also creates environmental challenges. Cities can form urban heat islands, which are areas that feel warmer. They can also concentrate pollution and stress water supplies.

To help, cities use public spaces like parks. These green spaces provide relief from the built environment. They also help mitigate the heat island effect. They can prevent carbon imbalances and help protect human health. Because of these impacts, the international community has prioritized sustainable cities through Sustainable Development Goal 11.