I'm don't feel like I really get the distinction between a mapping and a function, or a visualization and a graph. But he was careful to point out that it wasn

I'm don't feel like I really get the distinction between a mapping and a function, or a visualization and a graph. But he was careful to point out that it wasn't a graph. To me the key point is that the input is all three variables, the two points and their midpoint, and not just the midpoint.