So far, you’ve had a bird’s eye view of the motions. But it’s possible to just look along a single line(one dimension), rather than looking at a plane (two dimensions)
That all seems more special, because so many journeys are not along a single line, but many are across nearly flat surfaces (such as the Earth, at least over short distances). In other cases, we can draw maps to show the journeys on, and maps are usually two dimensional as well.