The diagram depicts ARC-IT as a set of layered viewpoints - each providing a different perspective to understand the architecture.
The approach to develop a System Architecture in this way is based on ISO/IEC/IEEE 42010:2011, a standard for "Systems and software engineering — Architecture description." This includes steps to define, not just data and messages, but the full environment in which the stakeholder concerns are satisfied. The figure to the right identifies the four Viewpoints used to describe ARC-IT: Enterprise, Functional, Physical, and Communication. While there is only one model per View, the models used result in a large number of diagrams per View. Only by considering all aspects of the model can one understand the scope of each Viewpoint and thus gain a complete picture the architecture.
Each Viewpoint includes a specification that describes the concerns addressed by that particular viewpoint. The accompanying viewpoint specifications also define the relevant model constructs, serving as a legend for the diagrams.
In addition to the four viewpoints, ARC-IT provides a fifth perspective: the ITS service package (formerly ITS application) perspective. This is not a viewpoint per se, but rather a way of looking at subsets of each view focused on a specific service or group of services. Service packages are derived from documentation like ConOps, System Requirements, standards, and other documents that have been written to describe parts of the Cooperative ITS environment. It should be noted that this is not an exhaustive list - new services will be developed over time and the architecture modified appropriately.
The Architecture Viewpoints are related through various correspondence rules.