Gray Code

The cells in Karnaugh map are arranged so that there is only a single-variable change (Gray code) between adjacent cells. Adjacency is defined by a single-variable change. A cell is not adjacent to the cells that diagonally touch any of its corners. Also, the cells in the top row are adjacent to the corresponding cells in the bottom row and the cells in the outer left column are adjacent to the corresponding cells in the outer right column. This is called wrap-around adjacency.