Did you get something like this?



We need a square's worth of circles (or a circle's worth of squares) so that choosing a single point will give us both location and direction.

Here a point along the labeled circle, which corresponds to a direction the bus is headed in, gives us a unique "slice," which is a solid square. A point in that square corresponds to a location in the parking lot. Or, going the other way, a position of the bus corresponds to exactly one point in this set, since both its direction and its location specify a slice and a point on that slice.

One minor detail: we have to agree on how to read points. If this one



is the east side of the parking lot, then this one



should be too, since all that has changed is the angle of the slice.

Can you draw the position of the bus corresponding to the given point?