It’s interactive data map time! This one’s a choropleth map charting each state’s combined state and local sales taxes for 2012. Data are from the Tax Foundation.*

The tutorial I developed for this data set for class today is based on the Mu Lin Multimedia Journalism Blog’s tutorial on Google Fusion Tables for beginners, in case you’re wondering where to start.

While I let Dr. Mu Lin’s post do the heavy lifting Tuesday, my contribution today was in guiding the class through some critical thinking about how to apply Fusion Tables, their understanding of how to interpret data, use color to create a clear visual order, and online usability.

How do you make sense of data by categorizing them? That question begets another: Am I trying to illustrate the range of a single set of data, such as population densities? Then using a range of greens or oranges or blues might be the way to go.

How do you select a color range that establishes a clear visual order? It’s a challenge to set aside our individual preferences and pick colors that help the data make sense. I love blues, greens and purples in art, but I have to set those preferences aside in favor of asking how to use colors to make outliers stand out or how to how to show gradual difference among related information.

How do you take advantage of interactive data mapping’s strengths vs. the limitations of static design for the print world? For instance, it might not be necessary to have the names of all states in a dynamic interactive map online because the name will appear in the popup box with data relevant to that state when the user clicks on it.
Of course, you also must ask how to make the map usable to everyone. People who have colorblindness have a right to read information online, too. I don’t know a lot about color blindness, beyond the fact that red-green is the most common form of it.

If you require guidance on such decisions, as I do, a site called Color Brewer 2: Advice for Cartography has an interactive color picker. You can select the number of categories, or “buckets,” you’re using, whether you need sequential, divergent or qualitative range of colors, and any special considerations such as publication for people with color blindness, for printing, or for photo copies.

* I am aware of criticism of the Tax Foundation. Economist Paul Krugman has called it “not a reliable source” if you’ve done a little fact checking on its demand to lower American corporate taxes. Interpretation is one thing; which data are used is another, and the raw numbers look sound. What we’re doing here is exploring it from an angle that affects everyday Americans who make retail purchases for everyday needs: combined base state taxes when combined with the average local sales tax in each state.

Corporations get a lot of attention when it comes to taxation because their decisions affect a lot of people, and their money gives them media attention and access to power. Journalists need to watch out for the interest of those who lack these advantages. So that’s why we’re looking into sales taxes in each state.

One limitation of this data set is that it comes from 2012. Lots of cities in Alabama raised local sales taxes in 2013. That’s not reflected in this exercise. Anybody want to take on the task of creating an updated one?