Last month I published a dashboard that analyzed Omaha’s recent Mayoral election. It employs a few advanced Tableau techniques including connecting to shapefiles and dashboard highlight actions, among others. You can find tutorials on many of these techniques already in the Tableau blog community, but I thought I’d share a less obvious technique I used in this viz that can really enhance a viz’s design quality. Without further delay, here’s a brief tutorial on how you can use one easy trick to make symbol maps pop in Tableau.
But first, what is a symbol map? Simply put, symbol maps place a mark (or symbol) on a background map based off of that mark’s longitude and latitude. The power of symbol maps lies in their ability to convey multiple layers of data through the symbols’ shape, size, and color.
Filled Circle Symbol Map
In this first iteration of my symbol map I use the filled circle shape to represent electoral precincts in Omaha. These circle are then sized by how many people cast votes at each location. You may have noticed that we have a small problem. In a few cases, precincts with fewer votes are overlapped by precincts with more votes.
Empty Circle Symbol Map
One way to solve this overlapping issue is to use an empty circle symbol map. Now we can see smaller precincts that were previously partially hidden by larger precincts. But what if we want some transparency but with thick borders that vary with how the precincts are colored? To do this we need to create a hybrid map.
Hybrid Dual Axis Symbol Map
To begin this hybrid map we first duplicate one of the pills in the columns or rows shelf (in this case I chose Latitude). This creates a copy of the map in the space below. Now I’ll change one of shapes to be the filled circle while the other one stays as the empty circle. At this point I also adjusted the opacity of the filled circles down a bit to around 80% opacity while leaving the empty circle symbol at 100% opacity (or 0% transparency). Now all we need to do is right click on one of the latitude pills and select “Dual Axis”.
And there we have it! A hybrid symbol map that beautifully blends the best of both previous symbol maps together into one eye-catching map. Now we can delineate where precincts are overlapping due to their transparency and accurately determine their underlying color based off of the marks’ thick border.
With Tableau’s custom shape repository, the number of dual axis shape shape combinations is limited only by your imagination. Have you used any other dual axis symbol combinations for extra flair in your work?