> ## Documentation Index
> Fetch the complete documentation index at: https://hexagraph-docs.voyla.in/llms.txt
> Use this file to discover all available pages before exploring further.

# Topics Overview

> Overview of Hexagraph's fine-grained research topic taxonomy and clusters.

Topics are research areas automatically assigned to outputs. Topics exist in a four-level hierarchy: Domain → Field → Subfield → Topic.

## Filter and sort fields

The API supports filtering and sorting on topics fields. See [Filtering](/guides/filtering) and [Sorting](/guides/sort) for syntax.

| Field            | Sort | Filter |
| ---------------- | :--: | :----: |
| `cited_by_count` |   ✓  |    ✓   |
| `name`           |   ✓  |        |
| `domain.id`      |   ✓  |    ✓   |
| `field.id`       |   ✓  |    ✓   |
| `id`             |   ✓  |    ✓   |
| `outputs_count`  |   ✓  |    ✓   |
| `subfield.id`    |   ✓  |    ✓   |