The three laws of great graphs
If you use graphs in your Powerpoint presentations, I hope you'll follow these three simple principles.
1. One Story
2. No Bar Charts
The only reason (did I mention only) to use a chart in a presentation is to make a point. If you want to prove some deep insight or give people textured data to draw their own conclusions, DON'T put it in a presentation. Put it in a handout. Give them a URL with a spreadsheet at the other end.
No, the reason you put a chart in a presentation is to tell a story. A single story, one story per chart. "Oh," the attendee says, "our costs are going through the roof!" Or, in the case of the picture here, "Oh boy LA and Florida are in big big trouble."
There is no room for nuance here. You don't have nuance in the other parts of your presentation, and it doesn't belong here.
If the facts demand nuance, don't use a graph, because you won't get nuance, you'll get confusion.
The problem with bar charts is that they should either be line/area charts (when graphing a change over time, like unemployment rates) or they should be a simple pie chart (when comparing two or three items at the same scale).
[I know full well that pie charts are not rigorous and often misused. My point is that if you need to show slight differences or many bits of data, you probably don't want a chart at all.]
The correct use of a bar chart is to show how several items change over a period of time. This, of course, demands nuance.
Here's the surprising one: You should animate your charts.
It's simple: create two slides. The first one shows where the data used to be, the second one, on the same axes, shows where it is or where it's going. Motion.
Establish the first slide. Make your point about your source and its validity. Then press the advance button. Boom.
There are 314 principles for good graphs and charts. But these three laws will take you far.