The Washington Meridian runs north on a longitude of 91°09′36″W from the base line, which is the Mississippi–Louisiana border at latitude 31° north. The Washington Meridian is the basis of cadastral surveys in southwestern Mississippi, south of the Choctaw Meridian base line and west of the territory of the Saint Stephens Meridian. The Washington Meridian shares the same initial point as the Saint Helena Meridian, which runs south from that initial point.