The forty-ninth parallel is the line of latitude that forms the boundary between Canada and the US from Lake of the Woods to the Strait of Georgia. The section from Lake of the Woods to the summit of the Rocky Mts was agreed to in the Convention of 1818, and that from the Rockies to the Strait of Georgia in the Oregon Treaty of 1846. As ultimately surveyed and demarcated, the boundary actually consists of several chords drawn between astronomically determined points on the curved parallel. The parallel also forms the first baseline for the Dominion Lands Survey System by which the territory that became the provinces of Manitoba, Saskatchewan and Alberta and some adjacent parts of British Columbia and Ontario was subdivided. It and the baselines every 24 miles (38.6 km) north of it are east-west survey control lines which are run as 6 mile (9.6 km) chords to curved parallels of latitude.