What Is a Network Diagram in Project Management

What Is a Network Diagram in Project Management?

Last updated on 10th Oct 2020, Artciles, Blog

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What are Network Diagrams?

Network Diagrams in project management are a visual representation of a project’s schedule. Well known complements to network diagrams include the PERT and Gantt charts. A network diagram in project management is useful for planning and tracking the project from beginning to finish. It represents a project’s critical path as well as the scope for the project. A good network diagram will be a clear and concise graphic representation of a project.

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How do Network Diagrams work?


There are two types of network diagrams: The Arrow Diagram and the Precedence diagram. The arrow diagram depicts nodes for events and arrows for activities. The precedence diagram depicts activities in the order they occur. If you work in IT you will most likely use the arrow diagram, depicted above. ‘A’ and ‘B’ each represent an event node. These event nodes refer to an instant when an activity is started or completed. An event node occurs only when all activities entering the node have been completed. The arrow represents the activity that takes place during the event. For example, if a task in a project were a “research competition’s ad campaign,” then the event nodes would designate the start and finish of this activity whereas the arrow would designate the activity itself.


Using the arrow and node method, you can depict project dependencies. In the diagram above, you see that Event C depends upon activities from Events A and B to be completed, and Event D depends upon Event C’s activities to be completed. Dotted lines with arrows represent “dummy arrows.” Rather than depict a dependency between two items, these arrows depict a logical relationship. Dummy arrows have no duration. They do not depict an activity. Instead, they transfer logic from one event node to another. Once the project is mapped out, you can write a key for the visual representation, listing the duration of events and activities. The network diagram will provide you and your project team with a full visual representation of your project.

When are Network Diagrams Used?

Network diagrams are used whenever project management occurs. Because these project management tools are so useful, they can help project management teams to visualize the planning they have put time and effort into. The diagram gives a quick-glance view of the project.It also demonstrates who is responsible for which tasks.

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.

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.


  • 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.

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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 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.

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