Table of Contents
MySQL 4.1 introduces spatial extensions to allow the generation, storage, and analysis of geographic features. Currently, these features are available for MyISAM tables only.
This chapter covers the following topics:
The basis of these spatial extensions in the OpenGIS geometry model
Data formats for representing spatial data
How to use spatial data in MySQL
Use of indexing for spatial data
MySQL differences from the OpenGIS specification
MySQL implements spatial extensions following the specification of the Open GIS Consortium (OGC). This is an international consortium of more than 250 companies, agencies, and universities participating in the development of publicly available conceptual solutions that can be useful with all kinds of applications that manage spatial data. The OGC maintains a Web site at http://www.opengis.org/.
In 1997, the Open GIS Consortium published the OpenGIS (R) Simple Features Specifications For SQL, a document that proposes several conceptual ways for extending an SQL RDBMS to support spatial data. This specification is available from the Open GIS Web site at http://www.opengis.org/docs/99-049.pdf. It contains additional information relevant to this chapter.
MySQL implements a subset of the SQL with Geometry Types environment proposed by OGC. This term refers to an SQL environment that has been extended with a set of geometry types. A geometry-valued SQL column is implemented as a column that has a geometry type. The specifications describe a set of SQL geometry types, as well as functions on those types to create and analyze geometry values.
A geographic feature is anything in the world that has a location. A feature can be:
An entity. For example, a mountain, a pond, a city.
A space. For example, a postcode area, the tropics.
A definable location. For example, a crossroad, as a particular place where two streets intersect.
You can also find documents that use the term geospatial feature to refer to geographic features.
Geometry is another word that denotes a geographic feature. Originally the word geometry meant measurement of the earth. Another meaning comes from cartography, referring to the geometric features that cartographers use to map the world.
This chapter uses all of these terms synonymously: geographic feature, geospatial feature, feature, or geometry. The term most commonly used here is geometry.
Let's define a geometry as a point or an aggregate of points representing anything in the world that has a location.