Mappings are simply dictionaries of name-value pairs, which allow you to make decisions based on variables such as which region the stack is being created in, or whether the environment is in production or development. You use the Fn::FindInMap function to access the contents of the mapping. Mappings have two levels of keys; there is a first level that has keys according to a top-level item, such as regions, and then a second level that allows you to define multiple subkeys, such as the operating system type in our previous example.