The Swimlane diagram has been around a 
while. As you might imagine the concept is based around dividing the page real estate into lanes that individuals or groups use to complete their tasks.
As the picture on the right shows, bands show clearly where individuals should stay to complete their work. In this case usually a race.
Applied to the process mapping world, swimlane diagrams are used to map roles to tasks, processes and decisions shown on the map. The following diagram shows how this works.
Roles mapped to individual tasks and decisions in a swimlane diagram. Courtesy Harvard Computing Group, Inc. Fundamentals of Process Mapping
While there’s a lot of logic to the concept of a swimlane diagram, they can become overly complex very quickly. For detailed maps where many roles and decisions are present, tasks or decisions are mapped to hand off points.
These are often off the map, or don’t follow a logical sequence of eye movement. The example above shows how much visual real estate can be wasted as a result. (More than 50% of this example is unused white space, yet it still hard to follow the cross over points).
