PostGIS

PostGIS is an open-source spatial database extender for PostgreSQL. It adds support for geographic objects to the relational database, enabling location-aware queries to be written in SQL and stored alongside other data. PostGIS implements the OGC Simple Features for SQL specification, providing a robust set of spatial types, functions, and indexing capabilities.

The core features include two primary spatial data types: geometry, which stores projected planar coordinates, and geography, which stores geodetic coordinates on the Earth’s surface. Spatial indexing is achieved through GiST indexes, which accelerate queries such as intersects, contains, and proximity checks. PostGIS exposes a broad library of spatial functions and operators (for example, ST_Intersects, ST_Contains, ST_DWithin) that cover topology, measurement, and transformation operations. It also supports coordinate reference systems via the PROJ library and handles SRIDs, transformations, and precision considerations.

Interoperability and data formats are strong points: PostGIS reads and writes common GIS formats and encodings, including WKT, WKB, GeoJSON, and supports various raster and vector workflows through integration with external tools. Although primarily a vector spatial database, it can work with raster data via optional extensions.

Architecture and ecosystem: PostGIS is installed as an extension within a PostgreSQL database, leveraging PostgreSQL’s reliability and features, and it integrates with popular GIS and web mapping tools such as QGIS, GeoServer, MapServer, and others. It is widely used in fields like urban planning, environmental management, and logistics for spatial analytics, data management, and web services.

History and license: PostGIS originated from academic and open-source GIS communities in the mid-2000s and is maintained by the PostGIS development team with contributions from the broader community. It is released as open-source software under the GNU General Public License.