Source: Adapted from P. Haggett (2001) Geography: A Modern Synthesis, 4th Edition, New York: Prentice Hall.
Each scientific discipline tries to offer a perspective from which the real world can be understood and interpreted. Transport geography, by seeking to understand mobility, focuses on the locations that generate and handle it, on the interactions of people, freight, and information, as well as the infrastructures set in place to support mobility. In many cases, the infrastructures, locations, and interactions are specific to a domain of freight or passenger circulation, but in many instances, they are shared (e.g. roads or airports that can be used for passengers and freight transportation alike).
There are key concepts related to transport geography, among which transportation networks, transportation nodes, and transportation demand are at its core. They form the transport system, which is linked to economic, political, regional, historical, and population geography, among others. Several other concepts, such as regional planning, information systems, operations research, and location theory are commonly used in transport geography, notably as tools and methods for the spatial analysis of transportation. At a wider level, links exist with several major fields of science, including natural sciences, mathematics, and economics. Like geography, transport geography is at the intersection of several concepts and methods initially developed outside the discipline that has been adapted to its particular interests and concerns.
The intersection, or the triangulation, of three concepts, can be used to define a general field of investigation. For instance, if one was to investigate transportation terminals, this subject would likely be at the intersection of the concepts of transportation networks, nodes, and demand. A transport terminal being an infrastructure part of a transport network that is fulfilling a demand from an origin to a destination. For a more general and complex concept, it is possible to expand the triangulation and include additional fields. Evaluating the environmental impacts of a transport project requires a triangulation of environmental studies, transportation systems, and spatial statistics and models. The above figure is not an exhaustive overview of all the fields related to transport geography, but a fair approximation of those involved and their relationships.