Let a and b be two nonempty * * *. If there is a unique element B corresponding to any element A in *** A according to a certain correspondence F, then such correspondence is called *** A to *** B, and it is marked as F: A → B. Among them, B is called A. A is called B's original image on the map F * * A, and the image with multiple elements is marked as f(A).

In mathematics and related fields, mapping or projection is usually equivalent to a function.

Mapping describes the special correspondence between two * * * elements in mathematics.

Maps have many names in different fields, and their essence is the same, such as functions and operators. What needs to be explained here is that a function is a mapping between two data sets, and other mappings are not functions.