Why DITA maps?

Maps allow scalable reuse of content across multiple contexts. They can be used by information architects, writers, and publishers to plan, develop, and deliver content.

Among the specific uses that maps support:

Defining an information architecture
The map can be used to define what topics are required for a particular audience and user goals, even before the topics themselves exist.
Providing an authoring interface
The map can be used as a starting point for authoring new topics and integrating existing ones.
Defining what topics to build for a particular output
Maps point to topics that are included in output processing. Authors or publishers can use maps to specify a set of topics to transform at the same time, instead of transforming each topic individually.
Defining online navigation
Maps can define the online navigation or table of contents for the topics it points to.
Defining what topics to print
Maps can define a hierarchy that will determine how topics will be combined and nested for printing.
Defining related links
Maps define relationships among the topics they reference; on output, these relationships can be expressed as related links among the topics in each relationship.