The 49th parallel is a circle of latitude that is situated 49 degrees north of the Earth's equatorial plane. It serves as a significant geographical marker, particularly in North America, where it forms part of the border between the United States and Canada. This line stretches from the Pacific Ocean in the west to the Lake of the Woods in the east. The 49th parallel was established as a boundary in the 1818 Treaty of 1818 between the United States and Great Britain. It was later confirmed in the Oregon Treaty of 1846, which resolved territorial disputes in the Pacific Northwest. This agreement helped define the northern border of the contiguous United States.