Visibility

Why
Visibility as a design principle is important because it allows the user to figure out how the design works through visual cues.

What
Visibility is the way a design looks and the elements of the design that give the user signals and clues about how to interact with the system.

Good Visibility

 * Correct parts must be visible
 * Correct parts must convey the correct message

Door Example
The door example considers the visual cues that go into a door. The door is simple and a good example because there is only one important element (the handle) and yet, there are so many ways to interact with a door.

The handle must obviously be visible but more important than that, the handle must convey a message about how to use the door. For example, putting a handle vertically suggests that the door should be pulled and putting the handle horizontally suggests that it should be pushed. Such signals that do not need any explanation and are processed subconsciously are called natural signals