Purpose of ditamap files
DITA map files are used for defining the topics of a publication, specifying the topic sequence, and controlling linking between topics.
Any topics referenced anywhere in the ditamap will be processed into the output publication.
In DITA, the sequence and hierarchy of the topics to be published are defined in the ditamap through nested topicref elements.
Relationship tables are used to store linking relationships between topics in a collection in the ditamap, rather than in individual topics. Linking relationships are defined in a table-like structure, with rows in the table determining which topics are linked to which.
DITA encourages the linking relationships to be stored outside the topic content. Links can be generated from topic hierarchies, relationship tables, and related-links section links.
Inheritance and cascades in ditamaps
Properties in ditamaps sometimes cascade from parent elements to child elements. Some values in ditamaps also override the equivalent values in referenced topics.
Embedded (or nested) ditamaps
The technique of using embedded, or nested, ditamaps can make it easier to manage documents by separating complex collections of topics into a number of smaller, simpler collections.
The bookmap feature
Bookmaps are a specialisation of the base DITA map information type. Like ditamaps, bookmaps are containers for structure and context metadata, and do not contain any content. Bookmaps are used to describe page layout publishing outputs such as books, articles, manuals and research papers. They contain information structures that are specific to linear publications, such as tables of figures, title pages, chapters, sections and parts.