Image sources: crafty.diply.com, cancerletter.com
Remember the old TV warning: Don’t try this at home? Well, many of us are home right now. And we are trying lots of new stuff. Like cutting our own hair or visualizing data. Both can be dangerous.
We’ve already talked about the limitations of COVID data and the importance of both broadcasting limitations when presenting data and seeking out such disclaimers when consuming data in any format. Charts, maps, and graphs attempting to show the severity of the pandemic across time and location run into many difficulties including differences in population sizes and densities, testing rates, and reporting policies of various states and countries. The result is a likely misrepresentation of reality. (For more on this, see The Covid Tracking Project at the Atlantic’s Visualization Guide.)
The misrepresentation can be even more severe when visualizations distort the data. Much of the distortion, intentional or otherwise, occurs along the X and Y axes.* So when designing or reading charts, pay attention to:
The order of values along the axes
Source:cancerletter.com
This graph, from the Georgia Department of Public Health's website, is now infamous. The original chart (see “Before” image) did not present the dates along the X-axis in chronological order. Moreover, the bars, which each represent a different county, were presented in different orders on different dates. The result “seemed to bend both time and place to achieve a clean descending-staircase effect,” wrote Morgan McFall-Johnsen at The Business Insider on May 17, 2020. The corrected version was later posted and, as you can see, told a different story. When presenting values that have an inherent order, such as dates, we should present them in that order such as earlier to later or lower to higher.
2. The span of values along the axes
It’s easy enough to choose the part of a chart that tells the story you want to tell and just omit the rest. So when you see a trend over time, always check the X-axis to see the span of time covered. If relevant time periods are not included, find out why.
3. The range of values along the axes
The lowest point on an axis is called the “origin.” It’s where the Y and X axes intersect. Much has been written about the importance of starting the Y-axis at zero because, when you don’t, you can make a small difference look like a big one. See the two bar charts here for a case in point.
4. The aggregation of values along the axes
When you combine values by computing sums, averages, counts, etc., it's called aggregating. The way values are aggregated along the axes can significantly affect the way the data look. For example, when using date values, consider how detailed of a story you want to tell. Do you want to show general trends or is it important to show the volatility over shorter intervals of time? The charts below show the same data at different levels of aggregation: week totals, month totals, and quarter totals.
Data visualizations, like charts, maps, and graphs, often use position to show the value of something. They usually do this using an intersecting X-axis (a horizontal line) and a Y-axis (a vertical line). Each axis shows a particular type of measurement such as dates, dollars, or miles or particular categories or groups. Lines, bars, or other shapes are positioned according to these measures and categories.
Let’s talk about YOUR data!
Got the feeling that you and your colleagues would use your data more effectively if you could see it better? Data Viz for Nonprofits (DVN) can help you get the ball rolling with an interactive data dashboard and beautiful charts, maps, and graphs for your next presentation, report, proposal, or webpage. Through a short-term consultation, we can help you to clarify the questions you want to answer and goals you want to track. DVN then visualizes your data to address those questions and track those goals.