Urban Models and Theories
This model, developed by E.W. Burgess, describes cities as a series of rings expanding outward from a central business district.
The Concentric Zone Model
This area at the center of most cities contains the highest concentration of commercial, financial, and retail activity.
The Central Business District (CBD)
This threshold percentage of the world's population now lives in urban areas, first crossed around 2007–2008
50% (More than Half)
These informal housing areas on the outskirts of cities in developing nations, characterized by makeshift shelters and lack of basic services, are known by this general term.
Squatter settlements (shantytowns / informal settlements)
This urban planning principle encourages higher-density, walkable, mixed-use development to reduce sprawl and automobile dependence.
Smart Growth
Homer Hoyt proposed this model in which cities grow in wedge-shaped sectors extending outward from the CBD along transportation routes
The Sector Model
Areas just outside the CBD characterized by older, often deteriorating housing and transitional land use
The Zone of Transition
These rapidly growing cities, found primarily in developing regions, have populations exceeding 10 million people.
Megacities
This term describes the outward movement of people and businesses from cities to surrounding suburban and rural areas.
Suburbanization
These urban boundaries, established by local governments, are designed to limit outward suburban expansion and protect surrounding farmland and open space.
Urban Growth Boundaries (Zoning)
In this urban model developed by Harris and Ullman, cities have multiple centers of activity rather than one single CBD.
The Multiple Nuclei Model
This term describes large-scale retail and commercial developments found at the edge of cities, often near highway interchanges.
Edge Cities
These cities serve as command-and-control centers for the global economy, housing major financial institutions, media headquarters, and multinational corporations.
World Cities (Global Cities)
Urban heat islands form when this type of surface material absorbs and re-radiates heat, raising temperatures in cities compared to surrounding rural areas.
Impervious surfaces (concrete, asphalt, pavement)
This design movement promotes walkable neighborhoods, mixed land uses, and traditional neighborhood design as alternatives to conventional auto-centric suburban development.
New Urbanism
This Latin American city model features an elite residential spine extending from the CBD, surrounded by zones of in situ accretion and squatter settlements on the periphery.
The Griffin-Ford (Latin American City) Model
Gentrification is the process in which this type of population moves into deteriorated urban neighborhoods, displacing lower-income residents as property values rise.
Higher-income / wealthier residents
This term describes the rapid and often unplanned urban growth occurring in many parts of Sub-Saharan Africa, South Asia, and Latin America, frequently resulting in informal settlements.
Overurbanization
This process, once practiced by banks and mortgage lenders, involved denying loans to residents in minority or low-income neighborhoods by literally drawing red lines around them on maps.
Redlining
This term refers to urban infrastructure designed to manage stormwater through natural processes like green roofs, rain gardens, and permeable pavement, reducing runoff and flooding.
Green Infrastructure (Green Space) (Greenbelt)
This economic theory explains why land values decrease as distance from the CBD increases, and how different land uses outbid each other at varying distances.
Bid-Rent Theory
This geographic phenomenon occurs when urban growth leapfrogs over undeveloped land to build farther out, contributing to inefficient land use and greater auto dependence.
Urban Sprawl
This demographic concept describes the movement of people from rural areas to cities and is the primary driver of urban population growth in the developing world.
Rural-to-urban migration
This term describes the phenomenon in which population and economic activity return to central cities after a period of decline, often driven by young professionals, arts districts, and urban revitalization investment.
Reurbanization (or Urban Renaissance) Revitalization
This planning strategy involves rehabilitating and repurposing previously developed or contaminated industrial land within existing urban areas for new uses, rather than building on undeveloped land at the urban fringe.
Brownfield redevelopment