Flow diagram

Flow diagrams are used to structure and order a complex system, or to reveal the underlying structure of the elements and their interaction.

Overview

The term flow diagram is used in theory and practice in different meanings. Most commonly the flow chart and flow diagram are used in an interchangeable way in the meaning of a representation of a process. For example the Information Graphics: A Comprehensive Illustrated Reference by Harris (1999) gives two separate definitions:

Flow chart or flow diagram... is a diagram that visually displays interrelated information such as events, steps in a process, functions, etc., in an organized fashion, such as sequentially or chronologically.

Flow diagram [is] a graphic representation of the physical route or flow of people, materials, paperworks, vehicles, or communication associated with a process, procedure plan, or investigation.

In the second definition the meaning is limited to the representation of the physical route or flow. An example of such a diagram is the illustration of the flows in a nuclear submarine propulsion system, which shows different streams back and forth in the system. The representation of such a system can be supplemented by one or more flowcharts, which show the sequence of one of the flows in one direction, or any of the control flows to manage the system.

The physical movement of objects from one location to another can also be visualized in a mix of maps and flowchart or sankey diagram, which are called flow maps. Flow maps can indicate on a map, what flows, moves or migrates, in which direction, and in which quantities etc.