Arrow Diagrams for Projects: Activity on Node & Activity on Arrow


The first step toward building a viable project schedule is organizing activities. One way to get organized is by using a network diagram. This is a tool for visualizing activities over the course of the entire project.

There are two main types of network diagrams: the arrow diagram and the precedence diagram. Let’s take a look at the former, also called activity on node or activity on arrow.

What Is an Arrow Diagram in Project Management?

Arrow diagrams are used in the planning stage of project management to schedule activities, which are represented by arrows, to better meet deadlines and use the right resources at the right time.

The tail of the arrow is the beginning of an activity, while the pointed end is representative of the endpoint of the activity. The length of the arrow reflects the time it will take to complete the activity (scaled to fit on the presentation chart).

These activities are connected at points called nodes, represented on the diagram by a circle. These connections indicate the order in which the activities must be done in the project schedule.

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Why Are Arrow Diagrams Important?

The arrow diagram is important for the project schedule because it leads to determining the critical path. The critical path represents the longest duration of every dependent task, and it’s used to find the most efficient schedule while still accomplishing the goals needed for a successful project.

Creating a schedule for a project is a way to organize tasks and know not only when they have to be executed, but which ones must be completed and which could be bypassed while still meeting the goals and objectives of the project. This is why an arrow diagram is so important. It leads to the best schedule for the project.

But arrow diagrams do more than just chart the best course from start to finish of a project. They also reveal scheduling and resource problems that might come up and how to resolve them. It can also show where additional resources might move the project faster toward completion!

Why Should Arrow Diagrams Be Made?

Using an arrow diagram lays out the steps necessary in a project or progress and the order they need to be executed. It shows the duration of each of those steps. Meeting the deadline is crucial for any project’s success and an arrow diagram assists in meeting those deadlines.

This technique makes it easier to figure out a sequence of events in the project, allowing project managers to drive efficiencies while meeting the timeframe of the project. It is a scheduling tool but also assists when monitoring the progress of a project. It is useful, especially when dealing with complex projects with many interrelated tasks.

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The Different Types of Arrow Diagrams

There are two different types of arrow diagrams: the arrow network (also called activity on arrow (AoA)) and the node network or activity on node (AoN), also known as a precedence diagram.

AoA Diagram

This is the diagram we’ve been talking about, one in which the activities are represented by arrows. These arrows are then connected by nodes, with the back of the arrow indicating the start of the activity and the front point the end. The length of the arrow is the duration of that activity, drawn in scale to fit on the diagram. This type of diagram only shows finish-to-start dependencies between activities.

AoN Diagram

In this type of diagram, the activities are represented by nodes. The nodes are then connected to one another by arrows. These arrows are used to show the relationship between the activities. Unlike the above diagramming, all four types of dependencies can be shown—finish to start, start to start, finish to finish and start to finish.

Activity on Node Diagram Example

Let’s illustrate this node diagram with a simple project—building a deck for a house. First, create a table of three columns. On the left is the name of the tasks and an ID number or letter, followed by a column listing the immediately preceding activity (IPA) and the final column will show the duration of the task in days or whatever time frame is appropriate. Our deck project would look like this:

task table to create arrow diagram

Next, create a box or node broken into two parts. One part has the name of the tasks and the other has the duration. Start on the left with a node with no activity before it. Then add an arrow moving to the right for the next node. If the activities can occur at the same time, such as submitting the permit and purchasing materials, then they are stacked. Therefore, our deck activity on node diagram would look like this:

Activity on Arrow Diagram Example

We’ll use the same project for the activity on arrow diagram and the same table as illustrated above. The basic concept is the same, but for an activity, the arrows represent activities on the diagram. Otherwise, the construction of this diagram is the same as above and looks like this:

Free Tools for Creating Arrow Diagrams

While these network diagrams can be created by hand, it’s not ideal. First, they change, and as they change a whole new diagram must be created. Secondly, using an online tool means the diagram will look more professional as well as be easier to read and share. Here are a few free tools to use to make arrow diagrams.

The free online tool makes a variety of different diagrams. There’s no signup required to use the software to draw. Create a diagram from scratch or use their drag-and-drop shapes on a template.

Google Drawings

Google Drawings Free (though a Google account is needed to use). Can draw shapes, arrows and more. Project managers can even collaborate with others on the tool and then export the finished diagram as an image file or publish it to the web.


This user-friendly diagram tool works online and offline and can make good diagrams as well as flowcharts, floor plans, technical drawings and more. The free version has most of the bells and whistles of the monthly subscription but can only save to their servers and exported in their format.

Best Practices for Arrow Diagrams

An arrow diagram is a scheduling tool, but it’s best to use only when there is some foresight as to how long each activity will take and what resources will be required to execute them. A clear picture of the logical sequence of those activities is needed.

Of course, the use of an arrow diagram is focused on the schedule of the project. Using this diagram for anything else is not going to get the same results— it’s only useful for project scheduling and the maintenance of the schedule.

The arrow diagram is a useful project management chart and it cuts through the complexity of a project, especially one with many dependencies. Know that, as good as an arrow diagram is, it can not be the only tool when scheduling a project. Project management software is more dynamic and integrates fully with the project.

How ProjectManager Helps You Map Processes

Using an arrow diagram will only get you so far when planning the schedule for your project. For one thing, it’s not part of your larger project management software. ProjectManager is an online tool that integrates scheduling with features that facilitate the execution of the plan to keep you organized and working more effectively.

Once you know your tasks, duration and sequence, upload that data into our tool. Open up our online Gantt chart, add the tasks and their start and end dates and you get a visual of the entire project on the Gantt’s timeline. Unlike an arrow diagram, you can link all four types of dependencies to avoid bottlenecks later on in the project.

A screenshot of a gantt chart in ProjectManager

Find the Critical Path

Nodes on the network diagram are like milestones and you can set milestones on the Gantt, too. They’re diamond-shaped icons marking the end of one project phase and the beginning of another or any important date. Then find the critical path by just filtering it on the feature.

The Gantt chart filtering for the critical path

Track Your Progress

You can’t assign tasks from an arrow diagram, but you can give your teamwork from our Gantt. Each task will have space for you to add descriptions, attach files and images, comment for collaboration, set priorities, deadlines and add tags. Outside of the Gantt are features such as a real-time dashboard for a high-level view of performance, resource management tools, timesheets and so much more.

ProjectManager’s dashboard view, which shows six key metrics on a project

ProjectManager is award-winning software that organizes tasks, teams and projects for greater productivity. Use our tool to plan, monitor and report on your progress and keep stakeholders informed. It’s the only tool you’ll need to drive your project to a successful end. Try it today with this free 30-day trial.