5.4 PostGIS database

PostGIS (/post'-jis/) is an open source software program that adds support for geographic objects to the PostgreSQL object−relational database. PostGIS follows the Simple Features for SQL specification from the Open Geospatial Consortium. As such, PostGIS includes:

Geometry types for points, linestrings, polygons, multipoints, multilinestrings, multipolygons and geometrycollections.
Spatial predicates for determining the interactions of geometries using the 3x3 Egenhofer matrix (provided by GEOS).
Spatial operators for determining geospatial measurements like area, distance, length and perimeter.
Spatial operators for determining geospatial set operations, like union, difference, symmetric difference and buffers (provided by GEOS).
R−tree spatial indexes for high speed spatial querying.
Index selectivity support, to provide high performance query plans for mixed spatial/non-spatial queries.

The PostGIS implementation is based on "light−weight" geometries and indexes optimized to reduce disk and memory footprint. Using light−weight geometries helps servers increase the amount of data migrated up from physical disk storage into RAM, improving query performance substantially.

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5.4 PostGIS database

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