The border starts in the north at the tripoint with the UAE; it consists of three straight lines: the first orientated NW-SE (91 km; 57 m), the second NE-SW (233 km; 145 m), and the third NE-SW (334 km; 207 m), terminating at the Yemeni tripoint. The border lies entirely within the barren Rub' al Khali desert, or 'empty quarter' of Arabia.[2] The Umm al Samim quicksand area also lies on the border, at the first ‘bend’ in the north.[3]