Consider this: a product is not complete until a person uses it. A chair is not complete until someone sits down; a shopping website, not until someone orders something. My first design teacher chose this idea to make a point: the product is there to be used by a person. What does he want to do with it? What does he do first? How does he get it done? What will he do next? Addressing these questions is interaction design.
Think about planning a room, let’s say a kitchen. Where do you put the groceries down when you come in? Can you reach the cupboards from the dishwasher? Do you eat here or somewhere else? Later you can choose the colors and finishes, but first you need to decide how you will use the room and where things should be. Such a plan is similar to interaction design.
Now think about software. Think about a mobile app for ordering pizza. What do people want to do? You decide they should be able to 1) Order their favorite pizza with one click; 2) Choose from a list of standard pizzas; 3) Order a pizza with the toppings they want. These options should be on the first screen. Should the standard pizzas be visible here? No, that’s too much scrolling, so you’ll show just the top three. Assembling a pizza from scratch needs its own screen because there are lots of great toppings. But how can people find what they want in a long list? When they’re done with the toppings and want to order a second pizza, what do they do?
Understanding, and imagining, what people want (and need) is the first step of interaction design. Understanding, especially of advanced software for complex applications, comes through research, such as interviews with target users, observation and analysis.
Defining the tasks and task flow is the next step. Think of a storyboard, or screenplay, of what people can do with the software. Unlike your favorite action film, it will probably not be linear, but involve branches and options.
Now you map the story to screens. Each task gets a screen or part of a screen. Sketches show the layout, or “floor plan”, of each screen or screen area. They illustrate what UI elements, such as lists, buttons and menus, will be used.
As these sketches become more detailed, you consider how users move from one screen to another, exactly how they work with the UI elements, and what data these elements contain. For example, a list showing the bill of materials for a 747 airplane must be designed differently than a list of pizza toppings. These detailed sketches are the final “deliverable” of interaction design.
Interaction design cannot exist in a vacuum; collaboration with product managers, researchers, software developers, visual designers and others is part of the job. At its best, interaction design is humble and invisible: the better it is, the less you notice it. Ideally it’s so natural that people don’t give it a second thought.