Don starts his book by describing two important characteristics of all designed products:
- Discoverability: Is it possible to even figure out what actions are possible and where and how to perform them?
- Understanding: What does it all mean? How is the product supposed to be used? What do all the different controls and settings mean?
He talks about common things that are often anything but discoverable and understandable, such as faucets, doors, and stovetops. One of my favorite quotes in the book is about faucets:
"If you want the faucet to be pushed, make it look as if it should be pushed."
Regarding doors, Vox published a great video on a particularly poorly-designed door on the 10th floor of the Vox Media office. The video references and even includes interview footage with Don Norman himself. And it’s funny. You should watch it.
It occurred to me that the typical stovetop design snafu has a direct translation into the world of data visualization. To explain, let’s start with the problem with stovetops. Ever turn on the wrong burner? Why? Because you’re stupid? No, because there are often poor mappings between the controls and the burners. The burners are often arranged in a two-by-two grid and the controls are often in a straight line, like this:
What does that have to do with data visualization? We often use similar controls—radio buttons, combo boxes, sliders, etc.—to filter and highlight the marks in the view. When there are multiple views in a visualization (a dashboard), there is a similar opportunity to provide clear, or natural, mappings.
Don gives the following advice for mappings:
- Best mapping: Controls are mounted directly on the item to be controlled.
- Second-best mapping: Controls are as close as possible to the object to be controlled.
- Third-best mapping: Controls are arranged in the same spatial configuration as the objects to be controlled.
Often the software default places the controls on the right-hand side. Here’s my attempt to show these options on a generic data dashboard, where the four different views are labeled A, B, C, and D, and the controls that change them are labeled according to the views they modify:
This is a relatively straightforward example, and the job of the designer of a more complex visualization is to make it similarly clear what can be done and how to do it. Designers use things like affordances, signifiers, constraints, and mappings to make it obvious. Note that it takes a lot of effort to make the complex obvious.