A map is a file that contains a hierarchical list of links to topics (topic references or topicrefs), something like the sitemap of a web site or the bookmarks menu in your web browser. A map represents the table of contents of a document, or a section of a document. When a map is published, the publishing process creates the final output by pulling together the topics that the map points to and converting them to a presentation format like HTML or PDF.
Maps can also contain references to other maps (map references or maprefs). For example, the map for a document can contain references to a different map for each section.
A bookmap is a special type of map that provides more control over book-oriented features, such as front matter, back matter, chapters, table of contents, appendices, and metadata.
Map files have a .ditamap extension, and are often referred to as DITA maps.