<!--lint disable no-html-->
<img src="https://github.com/radiantearth/stac-site/raw/master/images/logo/stac-030-long.png" alt="stac-logo" width="700"/>
[](https://circleci.com/gh/radiantearth/stac-spec)
## About
The SpatioTemporal Asset Catalog (STAC) family of specifications aim to
standardize the way geospatial asset metadata is structured and queried.
A "spatiotemporal asset" is any file that represents information about
the Earth at a certain place and time. The original focus was on scenes
of satellite imagery, but the specifications now cover a broad variety of uses,
including sources such as aircraft and drone and data such as hyperspectral optical,
synthetic aperture radar (SAR), video, point clouds, lidar, digital elevation
models (DEM), vector, machine learning labels, and composites like NDVI and
mosaics. STAC is intentionally designed with a minimal core and flexible
extension mechanism to support a broad set of use cases.
This is advantageous to providers of geospatial data, as they can simply use a
well-designed, standard format and API without needing to design their own proprietary one.
This is advantageous to consumers of geospatial data, as they can use existing libraries
and tools to access metadata, instead of needing to write new code to interact
with each data provider's proprietary formats and APIs.
The STAC specifications define related JSON object types connected by link
relations to support a [HATEOAS](https://en.wikipedia.org/wiki/HATEOAS)-style traversable
interface and a [RESTful](https://en.wikipedia.org/wiki/Representational_state_transfer) API
providing additional browse and search interfaces.
Typically, several STAC specifications are composed together to create an implementation.
The **Item**, **Catalog**, and **Collection** specifications define a minimal core
of the most frequently used JSON object types. Because of the hierarchical structure
between these objects, a STAC catalog can be implemented in a completely 'static'
manner as a group of hyperlinked Catalog, Collection, and Item URLs, enabling data
publishers to expose their data as a browsable set of files. If more complex query
abilities are desired, such as spatial or temporal predicates, the
**STAC API** [specification](https://github.com/radiantearth/stac-api-spec/) can be
implemented as a web service interface to query over a group of STAC objects, usually
held in a database.
To the greatest extent possible, STAC uses and extends existing specifications.
The most important object in STAC is an **Item**, which is simply a [GeoJSON](http://geojson.org) **Feature**
with a well-defined set of additional attributes ("foreign members"). The **STAC API**
extends the **[OGC API - Features - Part 1: Core](http://docs.opengeospatial.org/is/17-069r3/17-069r3.html)**
with additional web service endpoints and object attributes.
## Stability Note
This specification has matured over the past several years, and is used in
[numerous production deployments](https://stacindex.org/catalogs).
With the 1.0.0 release, implementors should expect that most definitions will remain
stable. Our goal
is to maintain backwards-compatiblity within the core for a long time.
The STAC specification follows [Semantic Versioning](https://semver.org/), so once
1.0.0 is reached, any breaking change will require the spec to go to 2.0.0.
## Current version and branches
The [master branch](https://github.com/radiantearth/stac-spec/tree/master) is the 'stable'
version of the spec. It is currently version **1.0.0** of the specification. The
[dev](https://github.com/radiantearth/stac-spec/tree/dev) branch is where active development takes place,
and may have inconsistent examples. Whenever dev stabilizes, a release is cut and we
merge `dev` in to `master`. So `master` should be stable at any given time.
More information on how the STAC development process works can be found in
[process.md](process.md).
## Communication
Our [gitter channel](https://gitter.im/SpatioTemporal-Asset-Catalog/Lobby) is
the best place to ask questions or provide feedback. The majority of communication about the evolution of
the specification takes place in the [issue tracker](https://github.com/radiantearth/stac-spec/issues) and in
[pull requests](https://github.com/radiantearth/stac-spec/pulls).
## In this Repository
This repository contains the core object type specifications, [examples](examples/),
validation schemas, and documentation about the context and plans for the evolution of the
specification. Each folder contains a README explaining the layout of the folder,
the main specification document, examples, and validating schemas.
Additionally, the [STAC API specification](https://github.com/radiantearth/stac-api-spec/)
provides API endpoints, based on the [OGC API - Features](http://docs.opengeospatial.org/is/17-069r3/17-069r3.html) standard,
that enable clients to search for Item objects that match their filtering criteria.
The **Item**, **Catalog**, **Collection**, and **STAC API** specifications are intended to be
used together, but are designed so each piece is small, self-contained, and reusable in other contexts.
- **[Overview](overview.md)** describes the three core object type specifications and how they relate to one another.
- **[Item Specification](item-spec/)** defines a STAC **Item**, which is a [GeoJSON](http://geojson.org) **Feature**
with additional fields ("foreign members") for attributes like time and links to related entities and assets
(including thumbnails). This is the core entity that describes the data to be discovered.
- **[Catalog Specification](catalog-spec/)** specifies a structure to link various STAC Items together to be crawled or browsed. It is a
simple, flexible JSON file of links to Items, Catalogs or Collections that can be used in a variety of ways.
- **[Collection Specification](collection-spec/)** provides additional information about a spatio-temporal collection of data.
In the context of STAC it is most likely a related group of STAC Items that is made available by a data provider.
It includes things like the spatial and temporal extent of the data, the license, keywords, etc.
It enables discovery at a higher level than individual Item objects, providing a simple way to describe sets of data.
- **[Examples](examples/):** The *[examples/](examples/)* folder contains examples for all three specifications, linked together to form two
complete examples. Each spec and extension links in to highlight particular files that demonstrate key concepts.
- **[Extensions](extensions/README.md)** describe how STAC can use extensions that extend the functionality of the core spec or
add fields for specific domains. Extensions can be published anywhere,
although the preferred location for public extensions is in the [GitHub `stac-extensions` organization](https://github.com/stac-extensions).
- **Additional documents:** The supporting documents include a complementary [best practices](best-practices.md)
document, and information on contributing (links in the next section). We also maintain a [changelog](CHANGELOG.md) of
what was modified in each version.
## Contributing
Anyone building software that catalogs imagery or other geospatial assets is welcome to collaborate.
Beforehand, please review our [guidelines for contributions](CONTRIBUTING.md) and [code of conduct](CODE_OF_CONDUCT.md).
You may also be interested in our overall [process](process.md), and the [principles](principles.md) that guide our
collaboration