Introduction to Axial Coordinates for Hexagonal Tile-Based Games.
Juwal Bose has posted another superb tutorial to Tuts+:
"The basic hexagonal tile-based approach explained in the hexagonal minesweeper tutorial gets the work done but is not very efficient. It uses direct conversion from the two-dimensional array-based level data and the screen coordinates, which makes it unnecessarily complicated to determine tapped tiles.
Also, the need to use different logic depending on the odd or even row/column of a tile is not convenient. This tutorial series explores the alternative screen coordinate systems which could be used to ease the logic and make things more convenient."