Understanding Arrow Diagrams: Examples and How to Make One [Step-by-Step Guide]

Arrow diagrams, also known as activity network diagrams or precedence diagrams, are a crucial project management tool used for scheduling activities and determining the critical path in a project. This comprehensive guide will explain what arrow diagrams are, provide examples, and walk you through how to make one from scratch.

What is an Arrow Diagram?

An arrow diagram is a visual diagramming method used to represent the required order of project tasks and scheduling dependencies between activities in a project plan. The diagrams show the network of tasks that need to be completed to speed up the project.

Arrow diagrams help project managers optimize schedules and resource allocation to determine the best schedule for timely project completion. The diagrams only show finish-to-start task dependencies and are created using circles, nodes to represent activities, and arrows to represent task sequences and dependencies.

Why Use Arrow Diagrams?

There are several benefits of using arrow diagrams in project management:

• Visualize the sequence of all activities that need to completed

• Understand scheduling constraints and dependencies between tasks

• Determine the critical path - the sequence of dependent activities that determines the project timeline

• Identify activities that can be delayed without extending the project finish date

• Optimize resource allocation between tasks

• Reveal paths for fast-tracking projects and crash critical activities

• Monitor project progress based on completed activities

In summary, arrow diagrams provide project managers with a bird's eye view of the entire project workflow so they can optimize the project plan for on-time completion.

Types of Arrow Diagrams

The two main types of arrow diagrams used in project management are:

Activity-on-Arrow Diagrams (AOA): Activities are represented by arrows connecting nodes (circles), with arrows indicating the sequence of activities.

Activity-on-Node Diagrams (AON): Activities are represented by nodes (boxes) connected by arrows showing the sequence and dependencies. Also called precedence diagramming method (PDM).

Both diagram types show the same information - just represented slightly differently. Activity-on-node diagrams are more common since they clearly separate nodes (activities) from arrows (sequences).

But arrow diagrams can get complex for large projects. Luckily, most project management software can automatically create precedence diagrams for you once task dependencies are defined.

Examples of Arrow Diagrams

Let's look at two examples that demonstrate activity-on-arrow diagrams and activity-on-node diagrams:

Activity-on-Arrow Diagram

This arrow diagram uses nodes (1-7) to represent start and end points, with labeled arrows representing the activities and their sequence. Activity B cannot start until A finishes, D cannot start until B finishes, and so forth.

The critical path is the longest sequence of dependent activities that determines the project timeline. In this example, the critical path is A-B-E-G. If activity E gets delayed, the entire project finish date gets pushed back.

Activity-on-Node Diagram

In this activity-on-node diagram, the activities are clearly separated into labeled node boxes (A, B, C). The arrows dictate the sequences and dependencies - activity B cannot start until A finishes, C can run concurrently after A finishes, and D starts after B & C complete.

The critical path here is A-B-D-F. If activity B gets delayed, the overall project will also get delayed unless actions are taken to fast-track subsequent tasks on the longest path.

These examples demonstrate how arrow diagrams provide a visual workflow of project activities and dependencies - making them easier to understand and optimize.

How to Make an Arrow Diagram from Scratch

Creating an arrow diagram takes five key steps:

Step 1. Identify All Activities

Make a comprehensive list of every single activity and task that needs to be completed for your project. The more detailed, the better.

Step 2. Determine Dependencies

Figure out the order of activities and which tasks depend on other tasks finishing first. Common dependencies:

• Finish-to-start (FS): Task 2 can't start until Task 1 finishes

• Start-to-start (SS): Task 2 can start at the same time as Task 1 starts

• Finish-to-finish (FF): Task 2 can't finish until Task 1 finishes

Step 3. Draw Nodes & Connect with Arrows

Draw circle nodes for start and finish points. Use boxes or circles for activity nodes - label all nodes. Connect with arrows based on sequences and dependencies.

Step 4. Confirm Critical Path

The critical path is the longest path of dependent activities determining the project finish date. If those activities delay, the overall project gets delayed.

Step 5. Review & Refine 

Double-check accuracy of sequences, dependencies, and timing. Refine diagrams as needed.

Let's walk through an example arrow diagram created from scratch using these steps:

Activity List

1. Create concept

2. Conduct market research

3. Assess business viability

4. Develop prototype

5. Test prototype

6. Gather funding

7. Manufacture product

8. Launch marketing campaign

9. Release final product

Key Dependencies

• Conduct research & assess business viability must happen before prototype development starts

• Prototype must be tested before manufacturing and release

• Funding must be secured before manufacturing and marketing 

Draw Diagram

• Start node

• Activity nodes for all 9 activities

• Finish node

• Arrows representing sequences based on dependencies

Confirm Critical Path

The critical path is the longest sequence: Create concept → Conduct research → Assess viability → Develop & test prototype → Gather funding → Manufacture product → Launch marketing → Release product

If the funding, manufacturing, or marketing activities face delays, the overall product launch will be postponed.

Review & Refine

Review all sequences and dependencies to confirm accuracy. Refine diagram as needed - you may identify parallel paths for fast-tracking.

This example summarizes the key steps for building an accurate arrow diagram from scratch. Having a detailed activity list and understanding task dependencies is crucial.

As projects get more complex with dozens or hundreds of activities, project management software comes in handy for automatically creating precedence diagrams after listing all tasks and durations in the tool.

Tips for Making Effective Arrow Diagrams

Here are some key tips to follow when creating arrow diagrams:

• Include every single activity and milestone

• Clearly determine finish-start dependencies early on

• Confirm the critical path dictating the overall project timeline

• Consider different graphical formats like AOA vs AON

• Use visualization tools like diagrams in project management software

• Update diagrams as changes occur to task sequences

• Review often to ensure accuracy and optimization opportunities

Thorough understanding of task sequences and scheduling dependencies is vital for making meaningful arrow diagrams. Treat them as living documents - continually review and refine them as projects progress.

Common Questions About Arrow Diagrams

Here are answers to some frequently asked questions about arrow diagrams:

What does an arrow represent in an arrow diagram?

Arrows represent the sequence of activities and dependencies between tasks in the project plan. The arrow direction shows which preceding activities must be completed before successor tasks can start.

What are the four types of dependencies in an arrow diagram?

The four main types of task dependencies shown in arrow diagrams include: Finish-to-start, Start-to-start, Finish-to-finish, and Start-to-finish.

What are dummy activities in arrow diagrams?

Dummy activities in arrow diagrams are tasks with zero duration that are used to connect multiple activity paths in the diagram or clarify sequences that might otherwise be confusing in complex diagrams.

Can I hand draw arrow diagrams or do I need project management software?

You can certainly hand draw arrow diagrams for smaller projects using sticky notes or whiteboards. But project management software comes with templates and automated diagram creation for larger initiatives.

Can I make arrow diagram templates to re-use?

Absolutely! Developing arrow diagram templates allows you to standardize models and re-use for similar project types. Templates save time compared to starting from scratch every time.

Key Takeaways

Arrow diagrams provide a graphical view of project schedules that allows optimizing sequences, crash durations, and resource allocation for on-time completion. Use them across project planning and monitoring.

Follow these core lessons when working with arrow diagrams:

• Map all activities & milestones with dependencies

• Understand the critical path dictating overall timelines

• Note paths for fast tracking and risk mitigation

• Treat diagrams as living models - continually refine

• Leverage arrow diagram templates for consistency

• Use project management software for complex projects

Relying solely on Gantt charts limits insights on scheduling sequences and constraints between tasks. Arrow diagrams fill this gap for project managers - improving workflows.