The function constrains the form.
How to evaluate a graphic:
If we accept that a graphic is a tool, what tasks is this one trying to help me with?
- The graphic must present several variables
- It should allow for easy comparisons
- It should organize the variables
- Is should outline correlations or relationships
For example if you were looking at an unemployment in the U.S. graphic, you should be able to decipher in less than 5 seconds:
- In which state has unemployment grown the most?
- In which state has it dropped the most
- Has the unemployment change been bigger in Michigan, Florida or California?
- Has unemployment dropped more in New York, New Jersey or Pennsylvania?
Once you’ve establish the goals of the graphic, you have to consider its shape.
Consider whether or not to compare using absolute variables or derived variables. For instance if you were comparing crime in a large and small city, you wouldn’t use absolute numbers because of course the larger city would have more crime. Instead you would divide crime by the city’s population then multiply by 100,000 to have the derived variable ‘crime per 100,000 people’.
Bursting the Bubble Chart
Bubble charts are not good for showing comparison because the human brain is not good at calculating surface sizes. It is better at comparing a single dimension such as length or height.
Always ask yourself: “What are users likely going to try to do with your tool (aka graphic)?”