MBRs are also an essential prerequisite for the [[R-tree]] method of [[spatial index]]ing.
==MBRs asAs spatial metadata==
Owing to their simplicity of expression and ease of use for searching, MBRs (frequently as "bounding box" or "bounding coordinates") are also commonly included in relevant standards for [[geospatial metadata]], i.e. [[metadata]] that describes spatial (geographic) objects; examples include [http://dublincore.org/documents/dcmi-box/index.shtml DCMI Box] as an extension to the [[Dublin Core]] metadata scheme, "Bounding Coordinates" in the [http://www.fgdc.gov/standards/projects/FGDC-standards-projects/metadata/base-metadata/v2_0698.pdf (U.S.) FGDC metadata standard], and "Geographic Bounding Box" in the (2003-current2003–current) '''ISO 19115 Metadata Standard''' for geographic information ([[ISO/TC 211]]). It is also (as "boundingBox") an element in [[Geography Markup Language]] (GML), that is utilised by a range of Web Service specifications from the [[Open Geospatial Consortium]] (OGC). In the '''ISO 19107 Spatial Schema''' (ISO/TC 211), MBR appears as the datatype GM_Envelope that is returned by the envelope() operation on the root class GM_Object.
Web-accessible articles that deal further with the concept of the MBR include "Unlocking the Mysteries of the Bounding Box"<ref>[http://purl.oclc.org/coordinates/a2.htm Douglas R. Caldwell: Unlocking the Mysteries of the Bounding Box]</ref> by Douglas R. Caldwell, and "Geographic Database Search Interfaces and the Equatorial Cylindrical Equidistant Projection"<ref>[http://chukchi.colorado.edu/PAPER/ Ross S. Swick and Kenneth W. Knowles: Geographic Database Search Interfaces and the Equatorial Cylindrical Equidistant Projection]</ref> by Ross S. Swick and Kenneth W. Knowles. The section on "searching" on the [http://geospatialmethods.org/searching.html Geospatial Methods] site is also well worth investigating. See also documentation for specific spatially enabled databases, e.g.,.<ref>[http://publib.boulder.ibm.com/infocenter/db2luw/v9/index.jsp?topic=/com.ibm.db2.udb.spatial.doc/db2sb16.html IBM DB2 documentation]</ref><ref>ESRI, 1993. Understanding GIS: The Arc/Info method. John Wiley and Sons</ref>
