@gregeganSF@johncarlosbaez It means that the distance the y axis was "given" in the diagram depended on how the x axis was set up. They only measure in one dimension, that you can move in, so things are relative to a fixed point. Think of it like drawing a map where your house is the origin and everything is described relative to your house. So things like "six blocks due east" are valid directions. Hope this helps!