Designing Navigation Systems

The SAP Design Guild has a good series on hierarchies: what they are, why users find them confusing, and how best to design and present them.

[…] hierarchies come in many guises and are present nearly everywhere: you find them in applications, hypertexts, Websites, portals, operating systems, or data collections. For example, files on a hard disk, documents in a Website, functions and options in an application, as well as a computerized part list can be organized as a hierarchy. Despite this ubiquity, many users are not as experienced with hierarchies as some developers might believe; in general people have problems understanding and using hierarchies, which are essentially an abstract notion and not a “real life” object.

(via Adam Kalsey)