An alphanumeric grid (also known as atlas grid) is a simple
coordinate system on a
grid in which each cell is identified by a combination of a letter and a number.
An advantage over numeric coordinates such as
easting and northing, which use two numbers instead of a number and a letter to refer to a grid cell, is that there can be no confusion over which coordinate refers to which direction. As an easy example, one could think about
battleship; simply match the number at the top to the number on the bottom, then follow the two lines until they meet in a spot.
Algebraic chess notation uses an alphanumeric grid to refer to the squares of a
chessboard.
[http://www.fide.com/fide/handbook?id=125&view=article ''Appendices'' in World Chess Federation Handbook: see part ''C.7'' of section ''C. Algebraic notation''. Retrieved 2010-03-22.]
Some kinds of
geocode also use letters and numbers, typically several of each in order to specify many more locations over much larger regions.
References
Coordinate systems