Yes. It goes mostly in one direction... [Realizes how unhelpful this is and tries to think of a better way to explain it.] In my world there's a long strip of land that circle it called the Red Line. That divides the world in half. Then the Grand Line crosses it, dividing the world into quarters. [Draws imaginary circle lines in the air.] The Grand Line is bordered by Calm Belts which no wind and thus make perfect breeding grounds for seakings. So the Grand Line really only goes in one direction: forwards from the "start" at Reverse Mountain. The end would be to reach around to the other side, but it's practically impossible. Only one man's ever done it before and come back alive.