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What Is a Network Diagram in Project Management?

Whether you’re a project manager or a project team member, you should familiarize yourself with network diagrams.

What is a network diagram in project management?

A network diagram is a graphical representation of all the tasks, responsibilities and work-flow for a project. It often looks like a chart with a series of boxes and arrows. It is used to map out the schedule and work sequence for the project, as well as track its progress through each stage, up to and including completion. Since it encompasses every single action and outcome associated with the project, a network diagram also illustrates the scope of the project.

A network diagram not only allows a project manager to track each element of a project and quickly share its status with others, but since research shows depicting data in a visual way can improve comprehension and enhance retention, a network diagram can also boost performance and productivity, while reducing stress among your team members.

Two types of network diagrams

There are two main types of network diagrams in project management: the arrow diagramming method (ADM), also known as “arrow network” or “activity on arrow”; and the precedence diagramming method (PDM), also known as “node network” or “activity on node.”

Arrow diagram method (ADM)

The arrow diagramming method uses arrows to represent activities associated with the project.

In ADM:

  • The tail of the arrow represents the start of the activity and the head represents the finish.
  • The length of the arrow typically denotes the duration of the activity.
  • Each arrow connects two boxes, known as “nodes.” The nodes are used to represent the start or end of an activity in a sequence. The starting node of an activity is sometimes called the “i-node,” with the final node of a sequence sometimes called the “j-node.”
  • The only relationship between the nodes an activity in an ADM chart can represent is that of “finish to start” or FS.

Occasionally, “dummy activities”—arrows that do not represent a direct relationship—need to be included in ADM network diagrams. In the diagram above, activity C can only occur once activities A and B are complete; in the network diagram, you’ve connected activity A to activity C. Perhaps we’re talking about tiling a floor (activity C): It can only begin once the concrete is poured (activity A) and the permits are obtained (activity B). Since activities A and B are not directly related—A doesn’t lead to B, and B doesn’t lead to A—you’ll need to draw a dummy activity between B and C to show that C is dependent on B being completed.An ADM chart also does not have a way to encapsulate lead and lag times without introducing new nodes and activities, and it’s important to note ADM is not widely used anymore due to its representational limitations.

Precedence diagram method (PDM)

In the precedence diagramming method for creating network diagrams, each box, or node, represents an activity—with the arrows representing relationships between the different activities. The arrows can therefore represent all four possible relationships:

  • “finish to start” (FS): This is used when an activity cannot start before another activity finishes.
  • “start to start” (SS): This is used to illustrate when two activities are able to start simultaneously.
  • “finish to finish” (FF): This is used when to tasks need to finish together
  • “start to finish” (SF): This is an uncommon dependency and only used when one activity cannot finish until another activity starts.

In PDM, lead times and lag times can be written in alongside the arrows. If a particular activity is going to require 10 days to elapse until the next activity can occur, for example, you can simply write “10 days” over the arrow representing the relationship between the connected nodes.

PDM network diagrams are frequently used in project management today.

Further reading: