Map file (ArcInfo)
MXD is a file extension for a map document used by ArcMap. ArcMap is a component of ArcGIS, a GIS (geographic information system) software suite.
GIS enables you to envision the geographic aspects of a body of data. Geographic information is specified in terms of geographic coordinates, such as latitude and longitude or some national grid coordinates, or through other identifiers such as street address, postal code, or forest stand identifier. A geographic information system can translate geographic data (such as a street address) into an explicit map location.
MXD files contain a map description, map layout, and embedded objects saved in the map. MXD files can be opened by ArcMap software.
Learn more about .MXD files:
Visit the ArcGIS web page.
Learn about Topology at ITKnowledgeExchange.com.
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