A map refers to a single input structure and an output structure.
A map can be used to operate on multiple types of documents within a single structure using the Input/Output (Multiple Input/Output Documents) mechanism.
When working with a map, you select map elements from the input or output panel. These elements are normally identical to the structure elements, and they cannot be modified or deleted (you have to change the structure elements for that). There are some cases when they might vary from the structure elements which are described at Validating a Map, Unrolling an Element from a Loop, and Splitting a Loop.
The properties associated with map elements are the properties of the corresponding structure elements. However, you cannot change these corresponding properties when working with a map. To change structure element properties, you must do so in the structure editor. In addition, you cannot add or delete map elements. In short, you cannot use the map editor to alter the definition of the map elements, as they must correspond to the structure elements.