How to Create Heat Maps

Published on November 5, 2015

This post is a continuation of the Creating Interesting Visuals series – click here to read the previous post on Radial Charts

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  1. Create a new visual using the “Stackexchange Daily Activity” dataset.
  2. Drag “Site” to the Y shelf, “Activity Date” to the Date shelf, and drag one of the measures (e.g., “Comments”) to the measures shelf.
    • Note: If you get a warning pop-up, the Activity Date field may be set to string and may need to be changed to date. On this page, you can click the “Activity Date” pill “Date/Time Functions->Date.”
  3. Click “Refresh Visual,” name the viz “Stack Exchange Daily Acitivity,” and click the orange “Save” button.
  4. Let’s say you want to show the darkness of each mark relative to each individual site, not across all sites as is the default. To do this, click the “Settings” button at the top right. This will bring up a settings popup. Click the axes tab and check off “Independent Scales,” then click “apply.”
  5. In the same Settings menu, you can change the color of the heatmap uses by clicking Palette. Choose one of the orange palettes. 
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  6. Your visual should look something like the following image. 
      image43  
  7. Next, change the heat map from displaying just “Comments” to an aggregate of all written activity. Click the “Comments” pill and click “Enter[]/edit Expression.” Enter sum([Answers] + [Questions] + [Comments]) as ‘Posts & Comments’.
  8. Click the orange “Save” button and click “Refresh Visual.”

Calendar Heat Map Analysis

Calendar heat maps are good for an initial look for potential seasonality and similar trends. They make a nice first exploratory step that you can then dig into more via more traditional line and bar charts.

What we can easily notice from this is that dba, gis, and stats all are primarily used on weekdays. This highlights their use as a professional resource. RPG by contrast has its activity spread into the weekend, which makes sense for a hobby site. GIS had a significantly more active second half of the year. DBA seems to have a similar occurrence, but this requires further visualization.

Creating Interesting Visuals is continued here – Creating Flow and Chord Charts