Simple Features for SQL

Simple Features for SQL
Name	Simple Features for SQL
Status	Published
Version	1.2.1
Year	2011
Organization	Open Geospatial Consortium
Related standards	ISO/IEC 13249-3, Well-known text representation of geometry

Simple Features for SQL. It is a formal standard developed by the Open Geospatial Consortium that defines a structured schema and a suite of operations for storing, retrieving, and manipulating two-dimensional geospatial data within a SQL-based relational database management system. The specification provides a common data model and a standardized set of SQL functions, enabling interoperability between different GIS software applications and spatial databases. Its adoption has been critical for the development of spatial database technology and underpins many modern geographic information system implementations.

Overview

The core purpose of the standard is to provide a consistent, vendor-neutral interface for geospatial data within the relational model. It achieves this by defining a set of geometry data types, such as points, lines, and polygons, which can be stored in table columns. The specification also standardizes a comprehensive collection of SQL functions for performing spatial analysis, including calculations for distance, area, and intersection. This allows software like Esri's ArcGIS, QGIS, and MapInfo to communicate uniformly with database systems like PostgreSQL with its PostGIS extension, Oracle Spatial and Graph, and Microsoft SQL Server. The widespread implementation of this standard has been instrumental in advancing open data initiatives and location-based service platforms.

History and standardization

The initial development of the specification was driven by the Open Geospatial Consortium in the late 1990s, with significant contributions from members like IBM and Oracle Corporation. The first version was formally adopted as an Open Geospatial Consortium Implementation Specification. It was later integrated into the international ISO/IEC standard ISO/IEC 13249-3, titled "SQL Multimedia and Application Packages - Part 3: Spatial." This dual standardization under both the Open Geospatial Consortium and ISO/IEC bolstered its credibility and encouraged adoption across the industry. Subsequent revisions have expanded its capabilities, with version 1.2.1 incorporating support for coordinate reference system identification and more advanced geometric constructs.

Data model and geometry types

The data model is based on a hierarchy of geometry types, rooted in an abstract `Geometry` class. The fundamental types include `Point`, `LineString`, and `Polygon`, which can be aggregated into collections like `MultiPoint` and `MultiPolygon`. Geometries are associated with a spatial reference system using a Spatial Reference System Identifier, ensuring coordinates are interpreted correctly on the Earth's surface. The standard also defines `GeometryCollection` for heterogeneous sets. These types are designed to represent real-world features, such as the location of the Eiffel Tower (a `Point`), the path of the Appian Way (a `LineString`), or the boundary of Yellowstone National Park (a `Polygon`). The formal definition uses concepts from computational geometry and topology.

SQL functions and operations

A key component is the standardized set of SQL functions for spatial querying and analysis. These are categorized into basic accessor methods (e.g., `ST_X()` for a point's coordinate), relational predicates (e.g., `ST_Intersects()`, `ST_Contains()`), and geometric operations (e.g., `ST_Buffer()`, `ST_Union()`). Functions like `ST_Distance()` can calculate the span between the Statue of Liberty and Times Square, while `ST_Area()` can determine the size of Lake Superior. The specification ensures that these functions produce predictable results across different systems, which is vital for applications in fields like urban planning, logistics, and environmental science. Support for spatial indexing via methods like the R-tree is also implied for performance.

Implementation and support

The specification has been implemented by most major commercial and open-source database management system vendors. PostgreSQL achieves compliance through the PostGIS project, which is widely used in organizations like the United States Census Bureau. Oracle Corporation implements it within Oracle Spatial and Graph, and Microsoft provides support in Microsoft SQL Server. Other implementations include SAP HANA and SQLite with the SpatiaLite extension. The Open Geospatial Consortium maintains a compliance testing program to ensure implementations adhere to the standard. The GEOS library provides a portable C++ engine used by PostGIS and QGIS to perform the underlying geometric computations.

Applications and use cases

Applications are vast and cross-disciplinary, forming the backbone of modern geospatial technology. In telecommunications, companies like Verizon use it for network planning and coverage analysis. Government agencies, such as the Federal Emergency Management Agency, utilize it for disaster response and floodplain mapping. The retail industry employs it for site selection and market analysis, while transportation authorities use it for managing infrastructure like the Interstate Highway System. It is fundamental to web mapping services provided by Google, Microsoft Bing Maps, and OpenStreetMap. The standard also enables scientific research in climatology, ecology, and archaeology, allowing the analysis of phenomena from deforestation in the Amazon to ancient settlement patterns near the Nile River.

Category:Geographic information systems Category:SQL Category:Open Geospatial Consortium standards Category:Data modeling