People are used to seeing data displayed in a usual and logical way. Not respecting the standards of data visualization can make your chart hard to understand, or even lead your audience to an incorrect conclusion.

Reversing axis

The Y-axis almost always rises from the bottom to the top of the graphic. Here is an example with a reverse Y-axis. It comes from an article in business insider and describes the evolution of gun deaths in Florida.

Disclaimer: I found this image on KD Nuggets

Since we are not used to seeing that kind of axis, it is quite hard to understand that the number of murders committed using firearms in Florida increased between the end of the 90’ and 2010. Even worse, a quick look at this graphic without paying attention to the Y-axis could lead to the wrong conclusion that the number of murders decreased in this period.

Cheating with colors

Here is a marketing email from Google. It describes the behavior of 41% of the customers, but the green part of the donut chart represents 59% of the chart, which is very misleading. Source: WTF Visualizations.