Consistency in design is the principle that when similar parts within a system are expressed in similar ways it makes using the system a much easier learning curve (Lidwell et al, 2003). Jared Spool like to ask the question of ““Will the user’s current knowledge help them understand how to use what I’m designing?” explaining that consistency in design draws upon the readers current knowledge of part of a system and then applies that knowledge to access another part (Spool, 2005). The four types of consistency are: Aesthetic, functional, internal and external (Lidwell et al, 2003).
Aesthetic consistency is subject to the visual appearance and style of the design, the elements that draw our attention, what we’re actually looking at. “Aesthetic consistency enhances recognition, communicates membership, and sets emotional expectations” (Lidwell et al, 2003). Aesthetic consistency ties back into the principle of Aesthetic usability in that “Attractive things work better”. (Donald Norman) Aesthetic consistency is when this attractive impression is repeated within similar parts of a system.
Functional consistency refers to just that, a parts function, how it works and the action it produces, which can improve usability and learnability as it draws on a persons existing knowledge about the design (Lidwell et al, 2003). Gaffney describes this type of consistency in his article on Why Consistency is Critical, “People have a strong memory for location, and your designs can leverage this characteristic by reserving particular locations for screen elements (navigation, search, login, content) and applying them consistently” (Gaffney 2005).
Internal consistency is the consistency between different parts within a system, which within a group is created through both aesthetic and functional consistency (Lidwell et al, 2003). “Internal consistency cultivates trust with people” (Lidwell et al, 2003), Rich Robinson, interactive designer at Skookum, describes consistency as your “firm handshake”, “design consistency gives you a level of professionalism or credibility … This is important for if you have some kind of an e-commerce website and you’re like, “All right. This is awesome. I’m going to take out my credit card. I’m going to buy your product.” You click “Buy Now” and it takes you to some crazy site that looks nothing like the page I was just on. My credit card’s going back in my wallet, and I’m going to go some place else.”
External consistency extends internal consistency to outside of the one system and relates it to elements in other separate systems, which is harder to achieve as it’s beyond the design element of the one system (Lidwell et al, 2003).
Consistencies aim is to make products easier for the consumer to use and so is crucial for design development.
Lidwell, W., Holden, K., & Butler, J. (2003). Aesthetic‐Usability Effect. In Universal Principles of Design(pp. 46). Massachusetts: Rockport.
Spool, J. (2005, September 15). Consistency in Design is the Wrong Approach . Retrieved from User Interface engineering: http://www.uie.com/brainsparks/2005/09/15/consistency-in-design-is-the-wrong-approach/
Gaffney, G. (2005). Why Consistency is Critical. Information and Design. Retrieved from http://www.sitepoint.com/why-consistency-is-critical/
Robinson, R. (na). Consistency in Interactive Design. Retrieved from http://skookum.com/consistency-in-interactive-design/