Nodes, Linkages and Urban Form

Two basic forms of interdependent nodes are at the core of the urban spatial structure:

Accessibility nodes. Relate to locations that transfer passengers and freight, thus offering accessibility to resources and markets within and/or outside the urban area. They include terminals such as ports, rail stations, airports and distribution centers. Most cities owe their initial development to a location that grants access to local, regional and/or international circulation, commonly a port site. Accessibility nodes are often dependent on the specific geographical requirements of each transport nodes, notably in terms of space consumption.
Economic nodes. Refer to locations that perform a function of economic significance. These functions are extremely varied and can include transformation, administration, education, retailing and leisure. Economic nodes tend to agglomerate, or to cluster, and are often dependent on access, if not close proximity, to an accessibility node or a linkage. Such clusters often take the form of central business districts, commercial strips industrial districts or logistics zones.

The presence of nodes requires linkages, which can be serviced by different transport modes. Road and transit linkages are obviously local in scope often taking the form of a grid that characterizes the form of many cities, while rail, maritime and air linkages integrate the city to a wider context of distribution and trade. The complex set of relationships between nodes and their linkages imply an urban form which is unique in each case.