The four major components of a GIS, encoding, management, analysis and reporting, have specific considerations for transportation:
- Encoding. Deals with issues concerning the representation of a transport system and its spatial components. To be of use in a GIS, a transport network must be correctly encoded, implying a functional topology composed of nodes and links. Other elements relevant to transportation, namely qualitative and quantitative data, must also be encoded and associated with their respective spatial elements. For instance, an encoded road segment can have data related to its width, number of lanes, direction, peak hour traffic, etc.
- Management. The encoded information is often stored in a database and can be organized along spatial (by region, country, census units, etc.), thematic (for highway, transit, railway, terminals, etc.) or temporal (by year, month, week, etc.) considerations. It is important to design a GIS database that organizes a large amount of heterogeneous data that can be easily accessed to support various transportation application needs.
- Analysis. Considers the wide array of methodologies and tools available for transport issues. They can range from a simple query over an element of a transport system (e.g., what is the peak hour traffic of a road segment?) to a complex model investigating the relationships between its elements (e.g., if a new road segment was added, what would be the impacts on traffic and future land use developments?).
- Reporting. A GIS would not be complete without its visualization and data reporting capabilities for both spatial and non-spatial data. This component is particularly important as it offers interactive tools to convey complex information in a visual format (displayed or printed). A GIS-T thus becomes a useful tool to inform people who otherwise may not be able to visualize the hidden patterns and relationships embedded in the datasets (e.g. potential relationships among traffic accidents, highway geometry, pavement condition, and terrain).
Information in a GIS is often stored and represented as feature classes (or layers), which are a set of geographical features linked with their attributes. On the above figure a transport system is represented as three layers related to land use, flows (spatial interactions) and the network. Each has its own features, related data and can be used independently or in combination with other layers.