Since urban areas involve specialized land uses having specific functions, each land use zone involves a set of relationships with other land uses. These relationships can be expressed by the mobility of passengers and freight since they represent a realized transport demand such as commuting (mobility of passengers) or supplying stores (mobility of freight). These relationships based on reciprocity are assumed by different transport systems involving transport operators that can be individuals, public or private companies. Overlaying all those relationships is close to an impossibility, but the most dominant relations usually involve large commercial, manufacturing, and transport terminal areas (such as ports and airports).
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, 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.
The most significant relationships between land use include:
- Commuting, mainly concerning passenger movements between residential areas and workplaces (central areas). It underlines reciprocity between labor supply and demand.
- Professional movements are related to work-based movements such as meetings that dominantly take place within central areas. They underline the reciprocity of economic activities.
- Personal movements include a range of activities that focus on shopping and social interactions. They underline the reciprocity between the supply and demand of goods and services.
- Distribution concerns a variety of freight movements to supply goods, such as procurement (supplying manufacturing activities), commercial deliveries, and home deliveries (e.g. e-commerce). They underline the reciprocity between activities generating and consuming goods.