The Design of Everyday Things

Affordances describe the relationship between objects and people, namely, what users believe are possible actions based on the physical properties of the object. Glass, for example, affords transparency and seeing through, but not passage. Some affordances are perceivable, while others are not.

Conceptual models are simplified (and not necessarily accurate) explanations of how things work. Conceptual models are often built on fragmentary information. However, good conceptual models allow users to predict the effects of their actions, even with simplified, incomplete information.

The term discoverability refers to the user’s ability to determine what actions are possible. Alongside understanding (i.e., how a product should be used), discoverability is a key aspect of good design.

Experience design is a branch of design focusing on the quality of the user’s experience and user enjoyment. The emphasis on users makes experience design an important part of HCD.

Feedback is a form of communication that alerts users that an action has been detected or processed. Fast, accurate feedback, such as a SENT message after sending an email, is central to HCD.

In contrast to traditional design, HCD is a design philosophy that places human needs and behaviors at the center of the design process. HCD ensures that designs match the needs and capabilities of their intended users. HCD has three areas of focus (experience design, industrial design, and interaction design) and results from a circular, iterative process based on observation, ideation, prototyping, and testing.

Industrial design is a field of design that focuses on optimizing the function, value, and appearance of products for the mutual benefit of users and manufacturers. Industrial design is one of the focuses of HCD, alongside experience and interaction design.

Interaction design focuses on how people interact with products. The aim of interaction design is to enhance users’ understanding of what can be done, what is happening, and what has just occurred. Interaction design draws on the disciplines of psychology, design, art, and emotion to ensure a positive, enjoyable user experience.

The term mapping refers to the relationship between the elements of two sets of things, such as the relationship between a light switch and a light bulb. Natural mappings use spatial analogies to enhance the user’s understanding of these relationships.

Semantics is the study of meaning. Semantic constraints are constraints that rely on the meaning of a situation to control possible actions. The only meaningful location for a motorcycle rider, for instance, is on the seat facing forward. Semantic constraints rely on external knowledge and can change with time.

Designers use signifiers to communicate how products should be used. Unlike affordances, which determine what actions are possible, signifiers communicate where actions should take place. A PUSH sign on a door is an excellent signifier because it is both clear and perceivable.