In a two-dimensional world simulation, for example the internal model of a robotics engine, or the representation of a world in a role-playing game, ground space is typically separated into a grid used to position items, similar to a game of chess (pawn to E4). I've seen this done both with grids of squares and with grids of hexagons.
What are the advantages and disadvantages each of using squares versus using hexagons as the basis for such a model?