Consistency in design refers to the similarity between different components to make the system more user-friendly. According to Lidwell(2010), there are four types of consistency in design; namely: aesthetic consistency, functional consistency, internal consistency and external consistency.
When a company logo or website is designed the font used and colours carefully chosen. This ensures a direct connection between users and the brand design. As a result of this, users associate a given set of emotions with a given design which may be reproduced across different objects for a similar brand. An example quoted by (Lidwell et al., 2010)is the Mercedes brand which fosters respect and admiration by the way its logo is prominent on the cars that it manufactures(Suh, 1990).
Functional consistency needs to occur when different objects and settings have similar roles. For instance, the symbols used to navigate analogue cassette tape players were transposed onto digital music players so that users could more easily adapt to a new medium (Mandel, 1997). Moreover, systems such as traffic signs and which have a specific colour sequence and arrangement, take advantage of functional consistency. The red light turns green, then flashes yellow; then turn red, in this specific order.
Internal consistency refers to when different elements in a given system retain the same colour scheme and general pointers. This enables users to easily navigate a given system with minimal knowledge. For instance, all the signs within a park would have the same colour and format to make them less confusing for users (Lidwell et al., 2010).
On the other hand, external consistency refers to elements within physically disparate systems having common elements (Galitz, 2007). For instance, the sign for a fire alarm would be similar within most buildings to enable any person to know how to find it, even if they were visiting a building for the first time.
Galitz, W. O. (2007). The essential guide to user interface design: an introduction to GUI design principles and techniques: John Wiley & Sons.
Lidwell, W., Holden, K., & Butler, J. (2010). Universal principles of design Retrieved from Ebook Library http://public.eblib.com/choice/publicfullrecord.aspx?p=3399678
Mandel, T. (1997). The elements of user interface design. New York :: Wiley.
Suh, N. P. (1990). The principles of design. New York :: Oxford University Press.