PostGIS – Frequently Asked Questions
PostGIS extends the capabilities of the PostgreSQL relational database by adding support for storing, indexing, and querying geospatial data. PostGIS features include Spatial Data Storage: Store different types of spatial data such as points, lines, polygons, and multi-geometries, in both 2D and 3D data.
Spatial Indexing: Quickly search and retrieve spatial data based on its location. Spatial Functions: A wide range of spatial functions that allow you to filter and analyze spatial data, measuring distances and areas, intersecting geometries, buffering, and more.
PostGIS extends the capabilities of the PostgreSQL relational database by adding support for storing, indexing, and querying geospatial data. PostGIS features include Spatial Data Storage: Store different types of spatial data such as points, lines, polygons, and multi-geometries, in both 2D and 3D data.
In essence, PostgreSQL is a database system that can store and manage any kind of data, while PostGIS is an extension that adds support for geospatial data to PostgreSQL.
PostGIS supports another kind of spatial data type called a raster. Raster data, much like geometry data, uses Cartesian coordinates and a spatial reference system. However instead of vector data, raster data is represented as an n-dimensional matrix consisting of pixels and bands.
So the data is stored in rows and columns. Because PostGIS is a spatial database, the data also has a geometry column with data in a specific coordinate system defined by spatial reference identifier (SRID).
Schemas are like folders, and can hold tables, views, functions, sequences and other relations. Every database starts out with one schema, the public schema.
Including all geometry information allows PostGIS to use EWKB as the format of record (e.g. in DUMP files). EWKB and EWKT are used for the “canonical forms” of PostGIS data objects. For input, the canonical form for binary data is EWKB, and for text data either EWKB or EWKT is accepted.
It turns out that PostGIS geometries are limited by the 1 GB limit. PostGIS stores all coordinates at double precision, so we need 16 bytes of storage space per vertex for a 2D geometries (24 bytes for a 3D geometry) in addition to the overhead of the geometry’s headers.
PostGIS is an open source, freely available spatial database extender for the PostgreSQL Database Management System (a.k.a DBMS).