Design hierarchy levels by what question each answers — domain, navigation, or selection
Before creating or reorganizing any hierarchical structure, ask what question each level answers—top level for domain identification, leaf level for specific item selection, and intermediate levels for navigation steps between.
Why This Is a Rule
Hierarchies are navigation structures: each level answers a question that moves you from "where am I?" to "there's what I need." When levels don't answer clear questions, navigation breaks — you open a folder, see 15 sub-folders, and can't determine which one contains what you're looking for.
The three level types correspond to three navigation questions: Top level answers "What domain am I in?" (Engineering, Finance, Personal). Leaf level answers "Which specific item do I want?" (the-specific-document, the-exact-note). Intermediate levels answer "Which subset narrows the search?" — each level should halve (roughly) the remaining options.
The critical insight: intermediate levels must answer questions that searchers ask during retrieval, not questions that made sense to the creator during organization. "Projects by date" makes sense during filing but is useless during retrieval if you search by project name. Design for the retrieval question, not the creation question.
When This Fires
- Creating a new folder structure, taxonomy, or hierarchical navigation
- Reorganizing an existing hierarchy that's hard to navigate
- When users can't find items in a hierarchy despite "logical" organization
- During any information architecture design for a knowledge system
Common Failure Mode
Creating intermediate levels based on how you created the content, not how you'll retrieve it. "2024/Q1/Week-3/" makes perfect chronological sense but is useless when you're looking for "the security audit results" — you'd have to know when you did the audit to navigate the hierarchy. Topic-based intermediate levels ("Security/Audits/") serve retrieval; time-based ones often don't.
The Protocol
Before designing any hierarchy: (1) For the top level, ask: "What broad domain identification question does this answer?" (2) For the leaf level, ask: "What specific selection does the user need to make at this point?" (3) For each intermediate level, ask: "What question does a searcher ask at this point during retrieval?" (4) If an intermediate level doesn't answer a clear retrieval question → it's a navigation dead-end. Remove it or redesign it to answer a question searchers actually ask.