The urban spatial structure considers the location of different activities in central areas and the periphery. A central area is a cluster of core and/or central activities and the most important central area of a city is usually labeled as the central business district (CBD). Core activities are those of the highest order in the urban spatial structure, namely tertiary and quaternary activities involved in management (head offices, finance, and insurance) and consumption (retailing). They commonly benefit from a high level of accessibility to the workforce and customers. Central activities focus on the functions of production and distribution with activities such as warehousing, manufacturing, wholesaling, and transportation. They require a good level of accessibility but need more land than core activities. Peripheral activities are primarily residential or servicing local needs.
Each city has its own history, but it is possible to derive a general common process in the evolution of the urban spatial structure:
- (A) Preindustrial city. For cities that existed before the industrial revolution, the CBD was limited to a small section of the city generally nearby the waterfront, the market, and/or a site of religious or political importance. These were locations where major transactions took place, including a marketplace, and thus required financial, insurance, warehousing, and wholesale services.
- (B) Mechanized city. With the industrial revolution came mass production and consumption. This enabled the emergence of a distinct retailing and wholesaling part of the CBD while manufacturing was located outside the core. Major terminal facilities, such as ports and railyards were also located in proximity to the city core and contributed to urban centrality. Managing these expanding activities also created an increasing need for office space located nearby traditional places of financial interaction. As the industrial revolution matured in the first half of the 20th century, major transportation axis spurred from the central area towards the periphery.
- (C) Mobile city. In the second half of the 20th century, industries massively relocated away from central areas to suburban areas, leaving room for the expansion of administrative and financial activities. The CBD was thus the object of an important accumulation of financial and administrative activities, particularly in the largest cities, as several corporations became multinational enterprises. These activities were even more willing to pay higher rents than retailing, thereby pushing some retail activities out of the CBD. New retailing centers emerged in suburban areas because of road accessibility and because of the growing suburban demand. Warehousing and transportation, no longer core area activities, also relocated to new peripheral locations close to modern terminal facilities such as container terminals and airports. The spatial structure of many cities became increasingly multicentric.