PrintBroadly speaking, the field of transportation is concerned with the transport of people and goods. To appreciate the value that GIS brings to transportation it is necessary to develop an understanding of the various forms of transportation that exist and also the types of activities and problems which those in the field need to address.
Transportation Modes
The different ways that people and freight can be transported are referred to as transportation modes. There are many different modes of transportation, and they can be differentiated and categorized in a number of ways. At a high level, we can divide transportation into the categories of air, land, sea, and space. We could further divide the land-based transportation into road, rail, pedestrian, bike, and pipeline, although one might rightfully argue that pipelines can run under the sea. Transportation modes are not always mutually exclusive and the specific modes we talk about often depend on the situation at hand. There have been many GIS applications which have been designed for a specific mode or for a group of closely related modes.
Transportation Processes and Activities
Just as we can categorize transportation according to the many modes of transportation which exist, we can think about transportation in terms of the many processes and activities which are performed in order to manage transportation infrastructure, vehicles, and operations. Some of these processes cut across modes and others are specific to a single mode or a few modes. These processes and activities include:
- infrastructure monitoring and maintenance;
- transportation planning and transit planning;
- property acquisition and management;
- vehicle tracking and logistics;
- highway safety analysis and improvement;
- traffic monitoring, modeling, and mitigation;
- screening projects for environmental impacts;
- dissemination of travel information to the public;
- reporting data to government agencies to secure funding;
- mobile data collection;
- routing and permitting of oversize overweight vehicles.
GIS-T plays an important role in enhancing the manner in which transportation organizations accomplish these processes and activities and, in some cases, allow organizations to perform functions which would simply not be possible without spatial technologies. GIS-T applications support evaluation of different scenarios, provide objective data for decision-making purposes, and promote the visualization of conditions.
GIS-T Techniques and Tools
GIS-T utilizes many mainstream geospatial tools and methods but it also employs a number of techniques which were borne out of the specialized needs of the transportation industry. These include:
- Conflation
Conflation is a technique used to bring together adjacent or overlapping datasets which were collected at different times and have different levels of accuracy and precision. While the process of conflation in GIS is frequently applied to transportation networks, conflation can also be used to combine other types of features. - Network Analysis
A roadway network is comprised of roads and intersections. In network terminology, the intersections are referred to as nodes, and the streets which connect the nodes are called edges. GIS-T commonly employs network analysis techniques to roadway networks to solve common transportation-related problems such as finding the best route between two points or determining the service area around a specific location (i.e., the area within which someone could reach the location of interest in a defined period of time). - Linear Referencing Systems
Linear referencing systems (LRS) are used to spatially reference the location of assets (e.g., bridges), occurrences (e.g., crashes), and roadway characteristics and administrative data (e.g., speed limits) by specifying the distance along a linear feature in a roadway network. Collectively, these attributes of a roadway are referred to as events. In this course we'll only consider the application of an LRS to roadway networks, they can be used in any linear network including pipelines and hydrologic networks. - Dynamic Segmentation
Dynamic segmentation is closely linked to LRS. In dynamic segmentation, we take the roadway events which are linearly referenced along roadways and transform them on the fly into spatial features. Taken together, LRS and dynamic segmentation allow us to effectively manage and utilize the myriad of attribute information associated with roadway networks. We will explore these techniques in detail in Lesson 6.
We will learn more about these techniques in upcoming lessons.