In DP4, maps are used to define the output from an application, and to accept input. The maps are displayed by the user interface manager at runtime, as they are requested by an application.
Maps are set up using a special editor, which you use to enter the display text and define the positions of the fields. You define maps in the same way for displaying screens and windows, and for outputting forms to a printer. Maps are stored and edited independently from application programs. If you change the text on a map, you do not need to recompile your application programs.
You can learn more about the DP4 user interface and maps here.