A Map Type is an abstract data type that defines the properties of map data structures. A Map (or Associative Array) is an abstract data structure composed of a collection of keys and a collection of values, where each key is associated with one value. The operation of finding the value associated with a key is called a lookup or indexing, and this is the most important operation supported by an associative array. The relationship between a key and its value is sometimes called a mapping or binding.