Transportation Geography and Network Science/Time Geography

Introduction
Transport geography is a sub-discipline of geography concerned about the mobility of people, freight and information, and its spatial organisation considering attributes and constraints related to the origin, destination, extent, nature and purpose of movements. Time Geography is considered a sub-group of social constructs created by Swedish Geographer Torsten Hägerstrand in the mid-1960s. By definition, time geography is a method of studying the coordination of human activities in the combination of society and nature. It involves environmental problems initiated by mankind and aims to develop knowledge which may better facilitate social and ecological sustainability. Time Geography uses the ideas of time and space in a bottom-up perspective to study how each person's daily activities are linked and coordinated with important geographical locations. Ultimately, time-geography leads to improved planning at all three levels (Urban, Regional and Global).

Background Of Transport Geography
Transport Geography can first be understood through a series of core principles which derive into the notion that there would be no transportation without geography and vice versa. These principles identify geographical attributes of information and transform them into an additional value in the process. Transport represents human activities worldwide as it allows for the mitigation of the constraint of geography both globally, regionally and in urban areas. It plays a role in the economic growth and spatial relationships between geographical regions. Transport creates links between regions and economic activities composed of four core components; Modes, Infrastructure, Network and Flows. These fundamentals help shape transport and geography even with ever-changing social, technological and economic variance.

Spatial Scale
Spatial Scale of Transport refers to the order of magnitude to the measurable extent of a land area or geographical distance studied or described. Transportation has such spatial constructs which are broken up into 3 categories.
 * Local is the spatial construct where the activity space is in the local scale representing a range of origins and destinations which individuals undertake within a time frame. Fixed Spatial constructs would be neighbourhoods or terminals which include flows of passengers and goods. These are generally grouped within the urban transport framework.


 * Regional where the spatial constructs of networks and flows tend to be more ambiguous and generally take the form of metropolitan areas and regions such as corridors


 * Global where the spatial constructs consider global networks and flows and have global value chains

Torsten Hägerstrand
Torsten Hägerstrand is a Swedish geographer who is primarily known for his work on migration, cultural diffusion and time geography. He received his doctorate at the Lund University and is highly renowned for his work in spatial planning. His investigation into Human Migration Patterns led to new understandings regarding paths of individuals as sequences similar to a movement chain. Socio-Environmental Mechanisms were also investigated, especially the relationship between natural and social science which in turn has led to the growth of the feminist behavioural geography movement. He studied conditions for individuals’ existence in different geographic, social, and ecological contexts by engaging new methods and cross-fertilising research fields; he developed precise concepts and a notation system which are generalised to describe any kind of individuals and are applicable at different levels of aggregation.

Origin
In Time-Space the individual describes the path within context however if we were to take the path of a lifetime, it becomes a network of constraints which are physiological and physical necessities or by public and private decisions. It’s a relationship between how individuals and populations are linked and will ultimately move (like migration) between locations. These constraints were then grouped into three categories:
 * Capability - limitations on the activity of individuals because of their biological structure and/or the tools they can command
 * Coupling - limitations that "define where, when and for how long an individual has to join other individuals, tools and materials similar to a critical path analysis
 * Authority - limitations on the time-space entity within which things and events are under the control of another individual or group.

Concept
The basic notion of time geography is the individual path which is tracked in the time-space diagram. The individual is an entity created purely for the examined time period and can be displayed in both 2D and 3D. Side-by-sideness (a) refers to individuals being together at a place for a time period for one's existence similar to coupling In-placeness (b) refers to the individual's existence over time's location for it is located at the same place for a time period. Encounter (c) refers to the part of an individual path meets another path Touch (d) refers to individuals being together at a place for a time period Separate (e) refers to either one of both individuals leaving the location where they met and stayed Front line of fabric refers to the present which is the only time there is an opportunity for any changes
 * Individual Path

Refers to an individual's behaviour in the space-time cube given their capability and coupling constraints Displays networks of individual paths in a graphical projection of space and time coordinates The conjunction of individual paths due to their capability and coupling constraints creating pockets of local order where the order is agreed upon and executed by individuals Refers to certain capability constructs of a given individual such as limited spatial size Authority constraints of a given individual or given group
 * Space-Time Prism
 * Space-Time Cube
 * Bundles of Paths
 * Concentric Tubes
 * Nested Hierarchies

Future Developments
Whilst these graphical representations of time-geography are essential, they do not provide the full picture but rather the foundation for how these concepts can increase the understanding in an ecological and sustainable method of how to develop mankind. Ultimately it is a product of the underlying ontology regarding large social-environmental mechanisms such as migration patterns. Social Sciences, Biological Sciences and Interdisciplinary Uses have been found as further usage of Hägerstrand's research into time-geography. His models and statistics were paramount in the development of the Geographic Information System (GIS) and the processes involved in visualizing movement data.

Geographic Information System
The GIS (Geographic information systems) utilized Hägerstrand's theory of Space-Time in the early 1990s incorporating temporal information and analytical functions such that it will be capable of handling both temporal and spatial data. GIS conceptually captured ontological constructs such as migration and movement and their relationship with space and time. With improvements in technology, it became possible to compute and visualize the theory and ultimately data. Time-Space GIS continues to be used in interdisciplinary and multidisciplinary faculties.

Legacy
Legacy of Hägerstrand's Time-Geography concept has continued use with the development in Time-Space GIS where it became possible to analyse various types of network datasets not limited to just geography but also of psychological behaviour and treatments.

Recommended Readings
Miller H. (2008) Time Geography. In: Shekhar S., Xiong H. (eds) Encyclopedia of GIS. Springer, Boston, MA Ellegård, Kajsa; Svedin, Uno (July 2012). "Torsten Hägerstrand's time-geography as the cradle of the activity approach in transport geography" Journal of Transport Geography. 23: 17–25.