Dual Axis (Layered) Maps in Tableau
Dual axis map is a map with two sets of geographical data overlaid on top of one another. For example, a filled map of different countries with data points for each country’s capital city layered on top.
A good example of a dual axis map is in the example below showing “Number of fatalities as a result of conflict around Africa” – In this map, we’ve shown both fatalities aggregated at country level as well as exact locations where these fatalities occurred.
You can access this map here
So, how can I create a dual axis map in Tableau?
To demonstrate this, I will be using Superstores data set to create a dual axis map showing a filled map of different states in US with data point for each city layered on top.
Step by step guide
Lets begin by building a filled map showing States by Sales
Drag State to details shelf
Drag Sales to color shelf
Chose Map under marks card
Duplicate the Longitude (generated) field as shown below
On the second Map, remove all dimensions and measures present.
Drag city to the detail shelf
Choose circle under marks card
Make the map dual axis
Adding Sales to the Size shelf of the second chart (circle) to resize the cities according to the Sales generated.
With this dual axis layered map, users can easily tell which State generated more Sales while at the same time tell the leading Cities within those high performing States or in other States.
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