The gross oversimplification of an encounter map is that it's a map at the level where token-level combat rules hold sway. In effect, it's where the boardgame aspects take over. The grid (rectangular, hex, or none depending on your system) is a convenience and its placement can have an impact on how the encounter plays out (for example, a grid placed so that an obstacle exactly fills squares may block movement, while one that's place half a square over on that same obstacle might allow movement through those squares).

And an elephant is like a snake.