# Canonical Concepts

As mentioned in the [Developer Guide](https://developers.google.com/public-data/docs/developer_guide), datasets
can reference concepts defined in other datasets. Google, in particular, has
created a set of "Canonical Concept" datasets that are useful in a
wide variety of cases. Among other benefits, linking to these allows one
to:

- Control how data are visualized (e.g., colors, units, etc.)
- Specify data annotations
- Define time points in a consistent way
- Make concepts mappable
- Reduce data entry when using common geographic concepts (e.g., countries)

These datasets are summarized in the table below:

| Dataset Name | Description | Links |
|---|---|---|
| **entity** | DSPL entity concepts | [Documentation](https://developers.google.com/public-data/docs/canonical/entity) [XML](https://developers.google.com/public-data/docs/canonical/entity_xml) |
| **geo** | World geographic concepts | [Documentation](https://developers.google.com/public-data/docs/canonical/geo) [XML](https://developers.google.com/public-data/docs/canonical/geo_xml) |
| **geo.us** | US-specific geographic concepts | [Documentation](https://developers.google.com/public-data/docs/canonical/geo.us) [XML](https://developers.google.com/public-data/docs/canonical/geo.us_xml) |
| **quantity** | Quantity concepts | [Documentation](https://developers.google.com/public-data/docs/canonical/quantity) [XML](https://developers.google.com/public-data/docs/canonical/quantity_xml) |
| **time** | Time concepts | [Documentation](https://developers.google.com/public-data/docs/canonical/time) [XML](https://developers.google.com/public-data/docs/canonical/time_xml) |
| **unit** | Unit concepts | [Documentation](https://developers.google.com/public-data/docs/canonical/unit) [XML](https://developers.google.com/public-data/docs/canonical/unit_xml) |

<br />

Follow the documentation links above for more details.

**Caution:** Some of the canonical concepts
documented here are not (yet) visualizable in the the Public Data Explorer. See
[this FAQ
item](https://developers.google.com/public-data/faq#canonical_concepts_visualization) for more details.

## Concept Relationship Graph

The following figure summarizes the documented canonical concepts. Each
node represents a single concept (color-coded by dataset) while the arrows
between concepts show inheritance relationships
(e.g., `quantity:count` extends
`quantity:quantity`). Clicking on a node in the figure will take
you to the documentation for the corresponding concept.

![](https://developers.google.com/static/public-data/images/canonical/graph.png)