The fourth of Jakob Nielsen’s ten heuristics — consistency and standards — is key to creating applications that make sense for users. Think about the websites and applications you use: they all rely on well-established conventions. Blue underlined text is clickable, the shopping-cart icon shows the items you plan to purchase, the site logo is in the top left corner, a magnifier-glass icon stands for search — these are all examples of conventions that are used all the time in digital products and that make users’ lives easier.
A Continuum of Consistency
To be easy to learn and use, systems should adhere to both internal and external consistency — they should use the same patterns everywhere inside the system and should also follow web-, platform-, and domain-specific conventions.
Internal Consistency
Internal consistency relates to consistency within a product or a family of products, either within a single application or across a family or suite of applications.
A family of products refers to several products, sold individually or as a group, produced by the same company under the same brand. Most application suites will list menu components in the same order (File, Edit, View, and so on) or will use consistent icons for the same functions across applications and familiar layouts for dialog boxes and modals.
Internal consistency within a single product or application can often be seen in colors and page layouts used. For example, an application may use orange as its primary color, which is then applied to all text links and primary buttons. It may also utilize modals that are designed with the primary button on the right and the secondary buttons on the left.
