Activity on Node Diagram: A Comprehensive Guide

Activity on Node (AON) diagram, also known as Precedence diagram method (PDM), is a type of network diagram frequently used in project management to depict the various activities involved in a project and their dependencies. An AON diagram shows the flow of work from start to finish and helps visualize the critical path of a project, which is the sequence of tasks that must be completed on time to ensure project completion within the designated timeframe.

Activity on Node Diagram: A Comprehensive Guide

In this comprehensive guide, we will cover everything you need to know about activity on node diagrams, including its definition, components, benefits, and how to create one.


Activity on Node diagram is a visual representation of project activities and their dependencies using nodes and arrows. The nodes represent individual project activities, while arrows indicate the dependencies between them. These diagrams are considered an essential tool for developing plans, scheduling resources, monitoring progress, identifying potential problems early, and managing risk throughout a project’s life cycle.

An AON diagram typically consists of nodes arranged in a logical order or sequence with lines connecting them based on their dependencies. Each node represents an activity or task that needs completing before progressing to the next phase in a project.


The activity-on-node (AON) diagram consists of several components that form part of its structure. They include:


These refer to specific tasks that require completion within the context of the project. They are represented by oval-shaped nodes placed along the horizontal bars in chronological order as per their occurrence.


Also referred to as lines/edges/pipes/connectors; these represent logical links between each activity or task required for successful completion — they usually point towards downstream successors- with no upward pointing arrow going into any starting node unconnected.


These are graphic representations used to depict each milestone event i.e., start and end dates milestones represented through empty rectangle-shaped nodes at either end of the chart.


Each activity in an AON diagram has a duration, which is the amount of time required to complete that task. The duration is typically indicated on the node in days or weeks and enables project managers to estimate when activities are likely to start and finish.


These show how each activity depends on other tasks in the project. They may be depicted by arrows connecting two or more nodes together, indicating dependencies between tasks.


The use of AON diagrams provides several benefits such as;

  1. Enhances Project Management – Using an AON Diagram helps keep things organized, tracks progress, and ensures that deadlines are met with ease while staying within budget constraints.

  2. Easy Identification of Critical Paths- An AON diagram makes it easy to identify critical paths regardless of the size or complexity of a project, thereby ensuring that resources can be allocated efficiently.

  3. Optimization of Resources- When used correctly, AON diagrams make it possible to optimize resource allocation, ensuring maximum efficiency throughout every stage of a project.

  4. Reduces Risk – By breaking down projects into smaller sub-tasks per activity; team members can quickly troubleshoot any issues without compromising other parts of the process.

  5. Improved Stakeholder Communication- The use of visual aids like AON diagrams makes it easier for stakeholders to comprehend project progress effectively and respond accordingly without ambiguity.

How to Create an Activity on Node Diagram

Creating an Activity on Node diagram follows three straightforward steps;

Step 1: Identify Tasks/Activities

This involves making a list of all activities involved in completing a specific task before grouping them into sequences relevant for achievement towards their realization.

Step 2: Depicting Activities

After defining each activity based on its level/type/location; assign oval nodes representing each milestone event with textbox summaries (activity names) along horizontal bars placed in chronological order (from left-to-right).

Step 3: Depict Dependencies

Sequences of activities (tasks) are connected with lines (arrows) representing how they relate to one another. Arrows flow from start to end points through different shapes, which may represent different types of dependencies – finish-to-start, start-to-start, finish-to-finish and start-to-finish.


Activity on Node diagrams is an essential tool for modern project management. They help understand the relationship between tasks/activities in a project, identify the critical path and manage resources accordingly. An AON diagram breaks down complex projects into manageable parts, reduces risk, improves stakeholder communication and increases productivity across the team.

Creating activity on node diagrams can be straightforward by following three simple steps; identifying tasks/activities involved in each phase of a project, depicting them as milestones along horizontal bars in chronological order using oval nodes mixed with dependencies represented by arrows between activities.


What is an activity on node diagram?

An activity on node diagram (also known as an AON diagram) is a type of project management tool used to visualize activities and their dependencies.

How does an activity on node diagram differ from a network diagram?

An activity on node diagram represents activities as nodes, while a network diagram represents activities as lines or arrows connecting nodes. AON diagrams tend to be more compact and easier to read than network diagrams.

What are the advantages of using an activity on node diagram in project management?

AON diagrams can help improve project scheduling, reduce delays, and identify potential bottlenecks or areas of risk. They also provide a clear visual representation of the project plan that can be easily communicated to stakeholders.

Can you explain the difference between a critical path and a non-critical path in an AON diagram?

The critical path refers to the longest sequence of dependent activities that must be completed in order for the project to finish on time. Non-critical paths are shorter sequences of activities that can be delayed without affecting the overall project deadline.

How do you calculate the duration of each activity in an AON diagram?

Activity durations can be estimated based on past experience, expert opinion, or statistical analysis. In some cases, it may be necessary to break down complex activities into smaller tasks for more accurate estimation.

Can you use an AON diagram for agile project management?

Yes, an AON diagram can be adapted for use in agile methodologies by breaking down tasks into sprints and tracking progress through each iteration. This allows teams to adjust course quickly based on changing requirements or other factors.

What software tools are available for creating activity on node diagrams?

Many popular project management software tools, such as Microsoft Project, Primavera P6, and Smartsheet, include features for creating AON diagrams. There are also standalone software solutions available, such as Lucidchart and Visio.

How do you identify critical activities in an AON diagram?

Critical activities are those which, if delayed, would cause the overall project timeline to be delayed. They can be identified by tracing the longest path through the diagram from start to finish, and noting which activities are included in that path.

Can you use color coding or other visual aids to make an AON diagram more easily understood?

Yes, using color coding or other visual aids (such as icons or shapes) can help emphasize key elements of the diagram and make it more intuitive for users. For example, critical activities might be highlighted in red while non-critical activities are shown in green.

How often should an AON diagram be updated during a project?

It is recommended to update the AON diagram on a regular basis (such as weekly or biweekly) to reflect any changes in activity durations, dependencies, or priority levels. This can help ensure that the project stays on track and stakeholders remain informed of progress.

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