Developing an information hierarchy

• Parent-child relationships
• Breadth vs. depth
• Brainstorming techniques

In designing a hierarchy, the information architect must consider the balance between breadth and depth. Breadth refers to the number of items at a given level. For example, in Figure 1, the breath of the first level in the hierarchy is five.

Depth refers to how many levels are in the hierarchy: Figure 1 has a depth of two levels (not including the home page).

The configuration of the hierarchy translates directly into the number of menu options presented to the user. Using the hierarchy in Figure 1, this banking site has the following main menu options:

• Accounts
• Loans
• On-Line Banking
• About Us
• Investor Info

Hierarchies can be characterized at one end of the scale as narrow and deep and at the other end of the scale broad and shallow. Is one type of hierarchy more usable than the other? Much discussion of optimal hierarchical structure has revolved around the so-called "seven plus-or-minus two" rule. This rule is based on an often-cited 1956 study on the limitations of human short-term memory (Miller 81-97). Designers following this rule keep the number of menu items to no more than about nine. This quote from Rosenfield and Morville is an example: "…try to follow the seven plus-or-minus two rule. Web sites with more than ten items on the main menu can overwhelm users" (38).

However, this practice represents a misinterpretation of the original study. Additionally, studies indicate users find information more quickly and with fewer errors with structures that are broad and shallow (Larson 32). On the web, there are many highly usable sites that break the so-called "seven plus-or-minus two" rule. For example Amazon.com features 16 top-level categories in its information hierarchy:

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