MySQL implements spatial extensions following the specification of the Open Geospatial 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 Geospatial Consortium published the OpenGIS® 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 OGC 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 specification 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, town district, the tropics.
A definable location. For example, a crossroad, as a particular place where two streets intersect.
Some documents 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. Here, the term most commonly used is geometry, defined as a point or an aggregate of points representing anything in the world that has a location.