Metaphor can also be applied through analogy even if the metaphor is not concrete in the user interface. When the number of possible actions exceeds the number of controls, some functions become invisible, resulting in complexity. Make Good Use of Mappings A mapping is the relationship between two things. The easier a mapping is to learn and remember, the easier a device will be to use. Use natural mappings where possible.
Natural mappings take advantage of physical analogies and cultural standards.
A device is easy to use when there is visibility to the set of possible actions actions, where the controls and displays exploit natural mappings. Mappings Provide Feedback Feedback is the act of sending information back to the user about what has actually happened as the result of his actions or about the state of the system. Well known concept in the science of control and information theory. As number of features increase, the use of feedback diminished Feedback can be presented visually or aurally. It may cost more to develop a complex phone with good feedback, but the trade-off is increase in usability.