A network diagram is a graphical representation of the sequence of project activities and the dependencies among them. There are two types of network diagrams, activity on arrow (AOA) and activity on node (AON). The most common network diagram uses the AON diagram technique, in which boxes represent activities. The complex and dynamic nature of development projects make this tool especially valuable because it helps the project manager identify the potential interactions of project activities that can be easily missed otherwise. The value of the network diagram is that it provides visibility and control over the project schedule. It also helps determine the total duration of the project and its critical path, or path with the longest duration.

 

The figure below shows an example of a project network diagram that includes the duration estimates and dependencies; the diagram also shows the dependencies among the activities and how these can form parallel paths.

 

 

The Critical Path is Path A, this is the path in the network diagram with the longest total duration (100 days). Activities on the critical path cannot be delayed, or the whole project will be delayed, unless the loss of time can be offset somewhere else on the critical path. To find the critical path, add up the duration of the activities for each possible path through the network, to determine which has the longest total duration. The difference between the longest total duration and the shortest path(s) is the total amount of float or slack for the noncritical path activities. Float or Slack is the amount of time that an activity or a task in a project network can be delayed without causing a delay to subsequent activities or tasks and the project completion date.

 

In project management, a critical path is the sequence of dependent tasks that form the longest duration, allowing you to determine the most efficient timeline possible to complete a project.

 

The critical path is in essence the shortest time a project can be completed, even though the critical path is the longest path on the project. It is not the path with the most critical activities or the shortest path on a project network diagram. There are cases in which a network diagram may have two critical paths that have the same total duration.  A benefit of Critical Path Analysis (CPA) is that it helps identify the minimum length of time needed to complete a project. Where there is a need to accelerate a project, the CPA will help identify which project activities you can compress or fast-track to accelerate and complete the project within the available time.

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