Network Diagram in Project Management: A Complete Guide

Network diagram project management: Key takeaways

• A network diagram visually represents project activities and their dependencies.
• It helps project managers understand the sequence of work and parallel activities.
• AON, AOA, and PDM are common approaches to representing project networks.
• Network diagrams help identify the critical path and float.
• Leads and lags help represent timing between dependent activities.
• Understanding network diagrams is useful for PMP certification exam preparation.

What is a network diagram in project management?

A network diagram (a.k.a. project schedule network diagram) is widely used in project management. Particularly when the project manager and project team are dealing with complex projects. Because the network diagram assists in mapping out tasks. With the tasks, project managers also can see the sequence, dependencies, and timelines. 

A network diagram is a visualization tool, similar to Kanban – but it works differently. A network diagram uses boxes or nodes for tasks and arrows to show the exact sequence and order of work. 

The structured layout of the network diagram helps in keeping the tasks required to complete a project in sync. 

In this article, we will provide you a comprehensive guide on network diagrams. Before we start with the topic, let’s understand the basics and understand what a network project is.

What is a network project?

A project network (also called a project network diagram or activity network diagram) is a visual flowchart that maps out the sequence, logic, and interdependencies of all tasks needed to complete a project. 

How does a network diagram work? 

As mentioned earlier, a project network diagram/activity network diagram is a visual flowchart. This flowchart displays all the tasks, durations, and dependencies within a project in an arranged manner. 

Instead of looking at activities as a simple list. A network diagram shows which activity comes before or after another activity.

For example:

A → B → C

• This means activity A must be completed before activity B can begin
• Activity B must be completed before Activity C

Why are network diagrams important?

Network diagrams allow project managers to:

• Understand activity dependencies
• Identify activities that can happen simultaneously
• Determine the sequence of project work
• Identify the critical path
• Estimate how changes to one activity may affect the project
• Support schedule development and analysis

Project network vs. network diagram

The terms are often used interchangeably, but a project network refers to the overall logical relationship between project activities, while the network diagram is the visual representation of those relationships.

What is a project schedule network diagram?

A project schedule network diagram is a network diagram that represents the logical relationships between activities in a project schedule.

It is created after project activities have been identified and their dependencies have been determined. The diagram helps project managers understand how the sequence of activities affects the overall project duration.

The schedule network diagram can help identify:

• The sequence of activities
• Activity dependencies
• Parallel activities
• The critical path
• Potential schedule constraints
• Activities that could affect the project completion date

Project schedule network diagram and critical path

One of the most important uses of a schedule network diagram is the critical path method (CPM).

By analyzing the network, the project manager can determine the longest sequence of dependent activities. This is known as the critical path.

A delay in a critical-path activity can potentially delay the overall project completion date.

Types of project network diagrams in project management

There are many ways to represent project activity relationships. Similarly, there are a few types in the project network diagram as well. 

Here we have explained all the types of network diagrams in project management. 

A. Activity-on-node (AON)

In an activity-on-node diagram in project management. Tasks/activities are represented inside boxes or nodes. The arrows show the logical dependencies and sequencing between them.

Here’s an example of an AON network diagram:AON is commonly used in project scheduling and is usually associated with PDM. We will learn about PDM further.

B. Activity-on-arrow (AOA)

In an activity-on-arrow diagram, activities are represented by arrows. While nodes represent events or milestones.

AOA is an older network diagramming approach compared to AON. Hence, AOA may use dummy activities to represent certain dependency relationships.

Here’s an example for AOA netword diagram :

C. Precedence diagramming method (PDM)

The precedence diagramming method is a technique used to build a project schedule network diagram. It is done by placing activities on nodes and connecting them with arrows to show logical relationships.

Here’s an example for PDM network diagram:

PDM supports four dependency types:

To make the explanation easier to understand. Let’s name the first task as “activity A”, and the second task as “activity B.” 

• Finish-to-start: Also known as FS, here activity (B) cannot start until activity (A) is completely finished.
• Start-to-start: SS is when the activity (B) cannot start until activity (A) has been started. It can either be at the same time or shortly after. They do not necessarily need to finish together. Activity (B) does not have to wait for activity (A) to completely finish either.
• Finish-to-finish: FF is when activity (B) finishes after activity (A) finishes. The two tasks can happen at the same time or overlap.  But activity (B) cannot cross the finish line before activity (A)
• Start-to-finish: In SF, activity (B) cannot finish until activity (A) has started. Although activity (B) can start before activity (A) does. It can run for a while, but it needs to wait until activity (A) officially wraps up.

These are all the types of dependencies. Also, FS is the most commonly used relationship in project management. 

Leads and lags in a network diagram

Dependencies do not always mean that one activity has to immediately follow another. In some cases, project managers use “leads” or “lags” to represent the actual timing between activities.

A lag is the amount of waiting time intentionally kept between two related activities.

For example, if a project requires two days of drying time after painting:

Painting → 2-day lag → Installation

A lead allows activity (B) to begin before activity (A) is completely finished.

Simple way to remember:

• Lead = overlap
• Lag = wait

How to create a network diagram in project management?

Creating a network diagram should connect the project activities with logical relationships and scheduled sequence. 

A project manager can follow these steps to create a basic network diagram. 

1. Identify the project activities

Start by listing all the activities required to complete the project.

For example, consider a website development project:

• A: Gather requirements
• B: Design the website
• C: Develop the website
• D: Test the website
• E: Deploy the website

2. Identify activity dependencies

Next, determine which activities need to happen before another activity can begin.

For example:

Requirements → Design → Development → Testing → Deployment

However, not every activity has to happen sequentially. Some activities can be performed in parallel depending on their dependencies.

3. Arrange the activities in sequence

Place the activities in their logical order and use arrows to represent their relationships.

Requirements → Design → Development → Testing → Deployment

4. Identify activities that can happen in parallel

If two activities do not completely depend on each other. But they can be performed simultaneously. 

Here, UI design and development can happen in parallel after the requirements are completed.

5. Add activity durations

Once the sequence and dependencies are established, add the estimated duration of each activity. This helps the project manager compare different paths through the network and estimate the overall project duration.

6. Analyze the network

The completed network can then be analyzed to identify the critical path, float, parallel activities, and activities that could affect the project’s completion date.

Project network diagram example 

Here’s an example of a project network diagram in project management. Hope this visual gives you a better understanding of the network diagram concept.

In this example, the UI design and development can begin after the requirements are completed. 

Since these two activities can happen in parallel. The project does not have to wait for one to finish before starting the other. 

Testing, however, depends on the preceding work and can begin only when the required activities are completed.

Critical path in a network diagram

The critical path is the longest sequence of dependent activities in the project network. It helps in determining the shortest possible project duration. All based on the current schedule logic.

Since path 2 has the longest total duration. It is the “critical path” for this example. Therefore, the shortest possible project duration in 13 days. Assuming the activity duration and dependencies remain unchanged.

What is the critical path in a network diagram? 

The critical path is the longest sequence of dependent activities in a project network. It determines the shortest possible time required to complete the project based on the current schedule.

In the example above:

Requirements → Development → Testing → Deployment

is the critical path because it takes 13 days, compared with 11 days for the other path.

A delay in an activity on the critical path can potentially delay the overall project completion date.

Important point for PMP aspirants

The critical path is not necessarily the path with the most activities. It is the path with the longest total duration.

What is float in a network diagram?

Float, also known as slack, refers to the amount of time an activity can be delayed without delaying the project completion date or, depending on the type of float, the early start of a successor activity.

In our example:

• Path 1 = 11 days
• Critical Path = 13 days

So, assuming there are no other constraints, the shorter path has 2 days of flexibility relative to the project completion date.

• Total Float: The amount of time an activity can be delayed without delaying the project completion date or violating a schedule constraint.
• Free Float: The amount of time an activity can be delayed without delaying the early start of its immediate successor.

Network Diagram vs Gantt Chart

Although both tools are used in project scheduling, they present project information differently.

A simple way to remember the difference:

• Network diagram: How are the activities connected?
• Gantt chart: When will the activities happen?

Advantages of a network diagram in project management

A network diagram helps project managers understand how project activities are connected. How those relationships can affect the overall project schedule. 

Some of its key advantages include:

1. Visualizes activities and dependencies

A network diagram gives the project team a visual view of the activities involved in a project. Also, the dependencies between them. Instead of reviewing activities as a long task list. The team can easily see which activities need to happen before others.

2. Helps understand the sequence of work

Network diagrams show the logical sequence of project activities. This helps project managers determine what needs to happen first and what can begin only after another activity has started or finished.

3. Identifies parallel activities

Some project activities do not need to be performed one after another. A network diagram makes it easier to identify activities that can happen in parallel.

For example, after completing project requirements, a team may be able to work on UI design and development at the same time. Identifying this parallel work can help avoid unnecessary delays in the schedule.

4. Helps identify the critical path and float

A network diagram allows project managers to analyze different paths through the project and identify the critical path. It can also help determine the float available for activities that are not on the critical path.

This helps the project manager understand which activities require closer monitoring and where there may be some flexibility in the schedule.

5. Helps identify schedule risks

When dependencies and activity sequences are clearly mapped, it becomes easier to identify activities that could create schedule problems.

For example, if an activity on the critical path is delayed, the project manager can immediately assess whether the delay could affect the planned project completion date.

6. Improves communication

A network diagram provides the project team and stakeholders with a shared visual representation of the project schedule.

It can make it easier to communicate:

• Which activities need to happen first
• Which activities depend on others
• Which activities can happen in parallel
• Which activities are on the critical path
• How a delay could affect the project

Network Diagrams for the PMP certification exam

Network diagrams are an important concept to understand when preparing for the PMP certification exam, particularly when questions involve project scheduling, activity dependencies, critical path, float, leads, and lags.

For the PMP certification exam, you should be comfortable reading a network diagram and using it to analyze the project schedule.

Network diagram questions in the PMP certification exam

You may encounter questions that ask you to:

1. Calculate the critical path.
2. Determine the total float of an activity.
3. Identify an activity that could delay the project.
4. Determine the relationship between two activities.
5. Calculate the effect of a lead or lag.
6. Analyze how a delay or change affects the project completion date.

A useful approach is to draw the network diagram first, identify all possible paths, calculate the duration of each path, and then determine the longest path.

PMP certification tip: Don’t identify the critical path simply by counting the number of activities. The critical path is based on the longest overall duration through the network.

Understanding network diagrams can make PMP certification questions related to critical path method (CPM), dependencies, float, and schedule analysis much easier to solve.

Conclusion

A network diagram helps project managers visualize activities, dependencies, and the overall project schedule. Understanding critical path, float, dependencies, leads, and lags can make schedule planning easier and is also useful when preparing for the PMP certification exam. With a clear understanding of these concepts, project schedules become easier to analyze and manage.

Frequently asked questions about network diagrams

Here are a few commonly asked questions regarding network diagrams.

1. What is a network diagram in project management?

A network diagram is a visual representation of project activities, their sequence, and the dependencies between them.

2. What is the purpose of a network diagram?

It helps project managers understand activity relationships, identify parallel work, analyze the schedule, and determine the critical path.

3. What are the main types of network diagrams?

The main approaches include activity-on-node (AON) and activity-on-Arrow (AOA). AON is commonly used with the precedence diagramming method (PDM).

4. What are the four types of dependencies in a network diagram?

The four dependency types are finish-to-start (FS), start-to-start (SS), finish-to-finish (FF), and start-to-finish (SF).

5. How is the critical path identified in a network diagram?

The critical path is the longest path through the project network and determines the shortest possible project duration.

6. What is float in a network diagram?

Float is the amount of time an activity can be delayed without affecting a defined schedule milestone or the project completion date, depending on the type of float.

7. Are network diagrams important for PMP certification?

Yes. Network diagrams are useful for PMP exam preparation, especially for questions involving critical path, float, dependencies, leads, lags, and schedule analysis.