Mapping: Prerequisites 
You map external fields to fields in the extract structure based on a data delivery agreement. This allows you to take market research data from external sources and map the information to internal fields, thereby allowing you to analyze the data.
You have completed the following prequisites:
Created and activated a data delivery agreement in the Customizing activity Define Data Delivery Agreements or Enhance Data Delivery Agreements
Assigned common fields in the Customizing activity Assign Common Fields to Data Set Types
By assigning common fields such as process ID, language, or currency to data set types, you complete the first step in defining the mapping of sources to targets.
For more information about the purpose of assigning common fields, see the documentation for this Customizing activity.