In the DITA standard architecture you create documents by collecting topics into maps.
A DITA map organizes a set of topics into a hierarchy. In most output formats, the structure of the map becomes the structure of the table of contents. Oxygen XML Editor provides support for creating and managing DITA maps through the DITA Maps Manager.
To watch a video on DITA editing and DITA Maps Manager view, go to http://oxygenxml.com/demo/DITA_Editing.html and http://oxygenxml.com/demo/DITA_Maps_Manager.html, respectively.
A book map is a specialized type of DITA map intended for creating the structure of a book.
You do not have to create an entire publication using a single map. It is generally good practice to break up a large publication into several smaller sub-maps that are easier to manage. You can include a sub-map in a main map using a mapref element. You can reuse sub-maps in a variety of different publications by including them in each of the different publication's main maps. The DITA Maps Manager provides support or creating and managing sub-maps.
By default, many output types place a single topic on each output page. In some cases you may want to output multiple topics as a single output page. To support this, DITA provides the chunk attribute on the topicref element in a map.