Lecture Notes for Feb. 7, 2007
Some Rules/Core Concepts
- A working definition of information: a difference (change, variation) that makes a difference (changes the message or meaning).
IF
Information is defined as a difference that makes a difference
THEN
All differences people can detect will be interpreted as meaningful
THEREFORE- Introduce no differences UNLESS they are meant to convey information
- Introduce no information that is not essential to the communication at hand
- Visually encoded information is context-dependent.
- In their book Designing Visual Interfaces: Communication Oriented Techniques, Mullet and Sano write that "[g]ood design ... ensures that significant design elements will be noticed by removing insignificant elements" (p. 39). We can translate that idea into this rule:
Designing means analyzing information to separate the significant from the insignificant:- Which details are essential?
- In what order/arrangement?
- How much contrast (size, weight, proportion)?
- What colors (hues, saturation)?
Visual Variables
- Visual variables: Jacques Bertin analyzed the perceptual system and determined that there are essentially seven visual variables, that is seven ways to create visual differences that human beings can detect and embue with meaning. Some people now add an eigth variable (time) to include animated displays of visual information.
- Bertin defines a mark as something that is visible and that can be used to make maps or graphs to show relationships in data sets. Marks can be made of points, lines, or areas.
- The variables define the set of transformations we can apply to a mark to create meaningful differences. Position, form (shape), orientation, color, texture, value, and size: these seven transformations provide the vocabulary for making visual statements.
- Visual variables also have properties that make each one appropriate (or inappropriate) for a given representational task. That is, some transformations of marks are well-suited to help people interpret graphic representations appropriately. There are five properties: selective properties, associative properties, quantitative properties, ordering properties, and length properties.
- Selective: whether variations can be easily distinguished from each other. A visual variable is said to be selective if a mark changed in this variable alone makes it easier to select that changed mark from all other marks.
- Associative: whether variations can be recognized as belonging to the same group even if the marks occur in different positions or with different orientations or have different shapes.
- Quantitative: whether variations can represent quantities (numeric values)
- Ordering: whether variations have a clear order (greater than, less than).
- Length: how many changes can be made while still being able to support the task. For example, how many different shades of gray can be used while still retaining confidence that each shade can be recognized as distinct from all the others. Some visual variables, such as position, have a more or less infinite length. Others, like intensity (value) are quite limited.