How to Overlay Charts in Tableau

Comparing two different datasets in separate charts can make an analysis feel disconnected. When you need to understand the relationship between two trends - like sales figures and profit margins over time - combining them into a single, cohesive visual provides immediate clarity. This guide will walk you through several methods for overlaying charts in Tableau, from the fundamental dual-axis technique to more advanced map layering, so you can build visualizations that tell a much richer story.

The Dual Axis Method: The Foundation of Overlaying Charts

The most common and powerful way to overlay charts in Tableau is by using a dual axis. This method is perfect when you want to compare two measures that share a common dimension (like time or location) but have different scales or units (like sales in dollars and shipping count as a raw number). A classic example is a bar chart of sales combined with a line chart showing the corresponding profit ratio to see how one influences the other.

Let's build one step-by-step.

Step 1: Build Your Base Chart

First, create the primary chart that will serve as the base of your visualization. For our example, let's create a bar chart showing monthly sales.

• Drag your date dimension (like Order Date) onto the Columns shelf. You can right-click the pill to set your desired time frame, such as Month.
• Drag your first measure (like Sales) onto the Rows shelf.
• In the Marks card, set the chart type to Bar.

You should now have a simple bar chart tracking sales over time.

Step 2: Add Your Second Measure

Next, introduce the second measure you want to overlay. Drag your second measure (like Profit Ratio) from the Data pane and drop it onto the opposite side of the Rows shelf, creating a second axis.

Tableau will automatically create a second chart directly below your first one, each with its own axis. You'll also notice a second Marks card has appeared - this is key, as it allows you to control each chart independently.

Step 3: Create the Dual Axis

Now it's time to merge them. Right-click the pill for your second measure (SUM(Profit Ratio) in our case) on the Rows shelf and select Dual Axis from the dropdown menu.

Look at that! Tableau has combined the two charts, layering one on top of the other with a second axis now visible on the right side of the visualization. The software will often default the new chart to a different mark type, such as circles in this case.

Step 4: Adjust Mark Types and Colors

The combined chart is functional, but let's make it clearer. You can now use the multiple Marks cards to format each visual layer separately.

• Select the first Marks card (for SUM(Sales)) and ensure its type is set to Bar. You can adjust the color or size here.
• Select the second Marks card (for SUM(Profit Ratio)) and change its mark type to Line. Pick a color that contrasts nicely with your bars.

Now you have a bar chart for sales with an elegant line chart for profit ratio overlaid, making the relationship between the two instantly recognizable.

Step 5: Synchronize Axes (When It Makes Sense)

This is a critical final check. In our example, we are comparing sales (dollars) with a profit ratio (percentage), so the scales are fundamentally different. It would not make sense to synchronize them.

However, if you were comparing two measures with a similar scale (e.g., Sales vs. Forecasted Sales, both in dollars), you must sync the axes to ensure the visual comparison is accurate. To do this, simply right-click one of the axes and select Synchronize Axis. If you skip this step, one bar could look much taller than another even if its underlying value is smaller, which can be very misleading.

Using a Combination Chart with "Measure Values"

What if you want to compare several measures that share the same scale? A dual-axis chart isn't the right fit because you'd get a confusing jumble of overlapping axes. Instead, you can use Tableau's built-in Measure Values and Measure Names fields to create a combination chart.

This approach works well for tracking three or four related metrics in a single view, like Sales, Profit, and Quantity over the same time period.

1. Drag your date dimension (Order Date) to the Columns shelf.
2. Drag the special Measure Values field from the Data pane to the Rows shelf. By default, Tableau will add all measures from your dataset to the view.
3. Find the Measure Values card that has appeared in your view (similar to a filter card). Drag out any measures you don't want to include, leaving only the ones you need (e.g., Sales, Profit, and Quantity).
4. Drag the Measure Names field onto the Color tile in the Marks card. This one simple action tells Tableau to give each measure its own distinct color and a corresponding entry in the legend.

You'll end up with a clean line chart showing multiple trends on a single, shared axis, providing context without the complexity of a dual axis.

Advanced Overlaying Techniques

Once you are comfortable with the dual-axis method, you can start creating more specific and visually engaging overlay charts.

Overlaying a Line on an Area Chart

This is a visually dynamic technique that's great for showing a cumulative total alongside a specific target or historical average. An area chart provides a nice sense of volume, while the overlaid line gives a precise point of comparison. The process is almost identical to our first dual-axis example - you'll just change mark types.

1. Build a base chart for Total Sales over time, but change the mark type on its Marks card to Area.
2. Add a calculated field for your Sales Target to the Rows shelf and select Dual Axis.
3. On the second Marks card, change this measure's mark type to Line.
4. Pro Tip: Select the Marks card for your area chart and click the Color tile. Lower the opacity to around 50-60%. This helps make your line chart pop and ensures no data points behind the area chart get obscured.

The result is a compelling visualization that shows performance beautifully against a target or benchmark.

Overlaying Geographic Data with Map Layers

For a long time, layering on maps in Tableau required clever dual-axis hacks. Thankfully, with recent updates, Tableau now supports true map layers, making it much easier to overlay geographic data.

Imagine you have a map showing sales by state (a filled map), and you want to overlay a marker for each state sized by its profitability. Here's how:

1. Create Your Base Map: Double-click a geographic field like State to create your base map. Drag Sales onto the Color tile to create a filled (choropleth) map.
2. Add the Next Layer: Drag your State dimension from the Data pane and hover it over the top-left corner of your map. A small box labeled "Add a Marks Layer" will appear. Drop the field there.
3. Configure the New Layer: Just like with a dual-axis chart, a new Marks card appears for this layer. On this new card, you can change the mark type to a circle, then drag Profitability onto the Size tile.

With just a few drags and drops, you now have an incredibly information-dense map showing both sales volume and profit size in one unified view. You can continue adding layers as needed, like point distributions for customers or store locations.

Quick Tips for Effective Overlay Charts

Combining charts is a great skill, but wielding it effectively requires some strategy. Keep these principles in mind:

• Focus on the Story: Don't combine charts just because you can. Make sure the combination answers a specific question, like "Does our increased marketing spend correlate with a rise in sales?" The goal is clarity, not complexity.
• Use Color and Opacity Wisely: Your chosen colors should make each layer easy to distinguish. High contrast is usually best. Don't be afraid to use the Opacity slider - it's one of the best tools for making overlapped data legible.
• Don't Overcrowd the View: A dual-axis chart with a bar and a line can be very clear. Add a second bar and a second line, and it will quickly become too busy to read. Less is often more.
• Leverage Great Tooltips: Instead of trying to label every data point directly on the chart, use the tooltip. The tooltip is the perfect place to present detailed information for both of your measures when a user hovers over a data point.

Final Thoughts

Mastering chart overlays - whether through a dual-axis, map layers, or combination charts - is one of the most effective ways to elevate your dashboards in Tableau. By thoughtfully combining visualizations, you move beyond showing simple metrics and start telling complete data stories that highlight relationships, correlations, and business insights in a single glance.

While techniques like these unlock powerful visual analysis, all the manual steps of dragging pills, managing multiple marks cards, and syncing axes can quickly consume your day. At Graphed we aim to transform that multi-step process into a simple conversation. Instead of learning where to click, you can just ask us to "compare sales versus profit ratio by month" or "create a dashboard showing Facebook Ads spend and conversions by campaign." We instantly generate interactive dashboards from your connected data sources, giving you back the time you’d otherwise spend wrangling reports.