In a hierarchical app, users navigate by making one choice per screen until they reach their destination. To navigate to another destination, users must retrace some of their steps—or start over from the beginning—and make different choices. Settings and Mail are good examples of apps that use a hierarchical structure.
In an app with a flat information structure, users can navigate directly from one primary category to another because all primary categories are accessible from the main screen. Music and App Store are good examples of apps that use a flat structure.
It’s no surprise that in an app that uses a content- or experience-driven information structure, navigation is also defined by the content or experience. For example, users navigate through a book by moving from one page to the next or by choosing a page in the table of contents; in a game, navigation is often an important part of the experience.
In some cases, it works well to combine more than one navigation style in an app. For example, the items in one category of a flat information structure might best be displayed in a hierarchy.