What is a Dual Axis Filled Map in Tableau? A dual axis filled map allows us to plot two maps or graphs on top of each other and encode values on both of them, but it shows up looking like one map. 

Why is a Dual Axis Filled Map in Tableau Useful:  

A dual axis filled map provides us with additional context to our visualization that we would not see if we only displayed data on one map. For example, with a dual axis map in Tableau we can see things like regional differences, as well as top performers within the region. 

Types of Questions a Dual Axis Filled Map Answers

  • What are the best performing regions, zones or territories? 
  • What is the top performing state within the regions? 
  • How does patient readmissions in one region or state compare to others?  

How to Do a Dual Axis in Tableau Using Filled Map

Key insight from this chart: In our chart, we see that the highest number of visitors came from the South region with a total of 1,706 unique visitors which also account for the highest re-admission rate of 33.7%. We can also tell that these numbers are driven by the state of Texas and should be our area of focus. We can also look at our individual states (circles) overall to find out the highest performing states that we need to pay attention to in terms of the number of unique visitors. In this case, California leads the way with 532 visitors. 

Next Step: We notice that although the West region has the 3rd highest number of unique visitors, it also has the lowest readmission rates. California is driving the numbers in that region; however, more investigation needs to be conducted here to see what is really going on in the other states. We’d want to consider doing some more training for our medical staff in those areas or get some data on clinic quality or customer surveys and correlate that with what we’re seeing here. 

How to Create a Dual Axis Tableau Map Using Filled Map Fast

This chart combines the Symbol map with a filled region map to create a dual axis map in Tableau. To create this chart, we first need to use the group function to tell Tableau how to color our regions.  

  1. Drag the State field to the rows shelf. 

  1. Hold the CTRL button on the keyboard and select the States that make up the West Region, then click the group icon. In this case we will select AZ, CA, CO, ID, MT, NM, NV, OR, UT, WA and WY. 

  1. Once they are grouped, you will notice that by default Tableau puts all the names of the States together as the group name. 

  1. Right-clicking this new group field and in the drop-down menu selecting Edit Alias. 

  1. Type in West as the new group name. 

  1. Repeat steps 2 – 4 for the other states to create our region groups. South: AL, AR, DC, DE, FL, GA, KY, LA, MD, MS, NC, OK, SC, TN, TX, VA, WV.  
    North East: CT, MA, ME, NG, NJ, NY, PA, RI, VT.  
    Mid-West: IA, IL, IN, KS, MI, MN, MO, ND, NE, OH, SD, WI.  
    For this tutorial, put MSP, HI and AK in one group and name them Other. We will filter them out. 

  1. Now notice that in the Dimensions pane a new field “State (group)” is added. Whenever we want to make any changes to our groupings, we can simply right-click on that grouping, and in the dropdown menu that appears select Edit Group. For now, we want to rename the new group and change it to Region. Right-click the group field and in the dropdown, menu select rename. Type in “Region” 

  1. Double click the Region group to create a Symbol Map. Tableau automatically generates a Longitude and Latitude field for your columns and Rows. 

  1. Drag your Region field to your filters shelf and exclude ‘Other’.  

  1. On your Marks card, change from ‘Automatic’ to a Filled Map by selecting Map. 

  1. Drag Region to the color shelf.  

  1. Your map should now look like this. But we need clean it up a little bit. 

Tableau Dual Axis Filled Map

Click on Map from the navigation menu at the top of our screen and choose Map Layers. 

Edit Map Layers in Dual Axis Filled Map Tableau

  1. On the pane that pops up, change the Washout value from 0% to 100%. 

Now your map should look like this with the light background removed to show only the region view. 

Now that we have our Region map, we need to add a Symbol map and then overlay the symbols by creating a dual axis in Tableau. To do this, we are going to duplicate either the longitude or latitude field generated by Tableau. 

  1. In your measures pane, hold down the control key and drag and drop your Longitude field next to the Longitude field in columns shelf. You should have two maps in your view. 

Adding a Symbol Map in Dual Axis Map Tableau

  1. Notice on the Marks card that we have two tabs for our maps. We are going to change one of these to a symbol Map.  

  1. Click on the tab for the second Map instance in the Marks card to open it. Change it from Filled Map to Circle by selecting it from the dropdown menu. 

  1.  Now remove Region from the color shelf in the second tab while making sure that Region is still on color in the other tab. 

  1. Locate your State field in your Dimensions and place that on your Details shelf in second tab. 

  1. Locate Number of Patients in the Measures pane and drop it onto your Size Shelf.  

  1. Make sure your results look accurate.

  1. Open the colored region map tab (the first tab) under the Marks card and Drag Number of Patients and Region to the Labels Shelf 

  1. Drag Region again and put it on the Details Shelf and then drag Readmission rate and place that on your Labels shelf.  

  1. Notice how you get an error message? This is because the Readmission rate field is calculated with a Table calculation. As a result, you need to tell Tableau how to compute the Readmission rate in this specific view. In this case, we want the Readmission rates to be computed using the Regions.  

  1. Hover on the Readmission rate calculate field and when the little arrow appears, click it to open the dropdown menu. Select Compute Using > Region. 

  1. This should fix the error and clear the error. Next, we need to combine these two maps into dual axis to complete our chart in Tableau. 

Combining Two Maps into a Dual Axis Filled Map Tableau

  1. Click the second Longitude field on your Column shelf and in the dropdown menu, select Dual Axis in Tableau. 

Awesome job! You’ve now learned another pro skill in Tableau. If you enjoyed learning how to do a dual axis filled map in Tableau, you are going to love our online individual course. We also offer corporate training online.