- Article
- 3 minutes read
- Reviewed August 3, 2026
WordPress taxonomies can be hierarchical, like Categories, or non-hierarchical, like Tags. The setting describes the relationship between terms and influences the default editor interface.
Choosing correctly helps editors understand whether terms form a tree or a flat vocabulary.
Hierarchical Taxonomies
A hierarchical taxonomy allows terms to have parents. This supports structures such as Country → Region → City or Product Category → Subcategory.
A child term usually represents a more specific concept within its parent, but WordPress does not automatically assign the parent when an editor assigns only the child.
Non-Hierarchical Taxonomies
A non-hierarchical taxonomy stores a flat set of terms. Terms may still be related conceptually, but WordPress does not record parent-child relationships between them.
This model works for topics, attributes, skills or keywords where no term consistently contains another.
Editor Interface Differences
WordPress normally displays hierarchical terms in a checklist and non-hierarchical terms through a tag-style input. Custom interfaces can change this presentation.
The interface should support the vocabulary size. A checklist with thousands of terms or a free-entry tag input for a controlled vocabulary can both create problems.
Assignment and Inheritance
Taxonomy hierarchy does not imply automatic content inheritance. Assigning an article to Málaga does not necessarily assign it to Andalusia and Spain.
Queries and templates must explicitly decide whether selecting a parent term should include content assigned only to descendants.
URL Structures
Term archives can use flat or hierarchical-looking URLs depending on rewrite configuration. The URL structure does not change the actual taxonomy relationships.
Deep paths can communicate context but make term moves more disruptive. Redirect old archive URLs whenever public slugs or parents change.
Multiple Classification Dimensions
Do not force independent dimensions into one hierarchy. A course taxonomy should not place Beginner, Marketing and Spanish in the same tree because difficulty, topic and language are different questions.
Use separate taxonomies when visitors need to filter by dimensions independently.
Choosing the Right Model
- Use hierarchy when terms naturally move from broad to specific.
- Use a flat vocabulary when terms are peers.
- Use separate taxonomies for independent dimensions.
- Consider term volume and the editor interface.
- Decide how parent and child queries should behave.
- Plan redirects before changing public term structures.
Examples
Good Hierarchies
- Geographic regions.
- Product categories.
- Documentation sections.
- Organizational divisions.
Good Flat Vocabularies
- Skills.
- Topics.
- Event features.
- Technologies used.
Frequently Asked Questions
Are hierarchical taxonomies the same as hierarchical post types?
No. Taxonomy hierarchy connects terms; post hierarchy connects content entries.
Does assigning a child term assign its parent?
Not automatically. Themes and queries may include descendants, but the relationship assignment remains explicit.
Can a taxonomy change from flat to hierarchical later?
Technically yes, but editors, terms, interfaces, queries and URLs should be reviewed before changing a live model.