People use the metaphor to help them to understand the world. An example is: "His heart is made of ice." Of course, we understand that the human heart cannot be made of ice. The ice can mean being unfriendly and thus being "cold", that is not welcoming. Mind maps can be drawn by using metaphors. You may draw a piece of ice at the heart of a young man to show his being cruel. In that sense, mind maps are nothing new and nothing special. Mind maps utilizes the power of metaphors, making things easily to understand. When you are not familiar with something, you may use the metaphor to make yourself more familiar with it.