-Define a national map.
-Define a local map.

The National Map is a collaborative effort of the United States Geological Survey and other federal, state, and local agencies to improve and deliver topographic information for the United States.

A local map is a transform that provides a hierarchical view of element transforms in a message map. You can use local maps to break up a large map into nested groups of mapping elements and process the complex elements of the whole data object. Local maps are a partial view of a larger map, rather than separate files.

Explanation: