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# Features API Overview

The Planet Features API offers Planet customers the ability to upload and save their Areas of Interest (AOIs) as features on the Planet platform and reference those features when making requests for data through the Planet Orders, Subscriptions, and Data APIs. Once a Feature is saved, it can be accessed as an [OGC-compliant Features API](https://ogcapi.ogc.org/features/).

The Features API is a great way to improve the efficiency of your data delivery workflows by enabling you to store your AOIs once and reference them, as needed, across the platform.

The Features API is available at the [Features API Dataset Root](https://api.planet.com/features/v1/ogc).

## Key Concepts

* **Feature**: A “thing” with a spatial location and geometry. In the API, the [GeoJSON definition of a Feature](https://datatracker.ietf.org/doc/html/rfc7946#section-3.2) is used. For example, a Feature could be a farm field polygon in South Africa.

* **Feature Collection**: A set of Features.

* **Feature Reference**: A reference (URL, ID) to a specific Feature.

### Limitations

* Only Polygon and MultiPolygon Feature types are supported
* Each Feature can have a maximum of 1,500 vertices
* Each organization can create up to 1,000 collections
* Each organization can create up to 2 million features across all collections
* Each collection can hold up to 150,000 features

## Feature References

Feature references are unique identifiers to specific features in your feature collection, which can be used as a reference to the feature geometry in supported Planet APIs (listed below).

Referring to a collection: `pl:features/{dataset}/{collection-id}`

Referring to a feature: `pl:features/{dataset}/{collection-id}/{feature-id}`

### Get a Feature Reference ID

The feature reference ID can be accessed for an individual item in the properties of the particular feature with the key `pl:ref` The reference ID is helpful for referencing your features when making requests to the Planet delivery APIs. See [Retrieve a feature](https://docs.planet.com/develop/apis/features/uploading-and-validating-features.md#retrieve-a-feature) documentation for an example on how to make such a request.

Use the reference ID when making requests to Planet Subscriptions, Orders, and Data APIs so that you don’t have to pass in the GeoJson each time. See below for examples on how to use them with each of these APIs.

### Using Feature References in the Planet APIs

You can use feature references in place of GeoJSON in the following Planet APIs. For more information, see the documentation for each API.

* [Data API](https://docs.planet.com/develop/apis/data.md)
* [Orders API](https://docs.planet.com/develop/apis/orders.md)
* [Subscriptions API](https://docs.planet.com/develop/apis/subscriptions.md)

### Feature Properties

When features are created and stored in the Features API, the system automatically generates and attaches several properties to each feature. These properties are available in the feature's `properties` object and are prefixed with `pl:`.

| Property  | Type   | Description                                                                                                                                                                                                                                          |
| --------- | ------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `pl:ref`  | string | Unique reference identifier for the feature. See [Feature References](#feature-references).                                                                                                                                                          |
| `pl:area` | number | The area of the feature in square meters, calculated using the [Cylindrical Equal Area (CEA) projection](https://en.wikipedia.org/wiki/Cylindrical_equal-area_projection). At the collection level, this aggregates as the sum of all feature areas. |

## Rate Limiting

To improve the experience for all users, Planet uses [rate limiting](https://docs.planet.com/develop/rate-limiting.md) to prevent overloading the system.

The Features API is rate limited to 5 requests per second.