What docs the imaginary line passing through Lake Ontario, Lake Erie, Lake Huron and Lake Su perior represent?

The imaginary line passing through Lake Ontario, Lake Erie, Lake Huron, and Lake Superior represents the international boundary between the United States and Canada [t3, t5]. This maritime border was established and refined through various treaties, such as the Treaty of 1908, and is managed by the International Waterways Commission [t5, t6]. Geographically, this line serves as the southern boundary of Canada for much of its eastern and central regions, separating the Canadian province of Ontario from several U.S. states including New York, Pennsylvania, Ohio, Michigan, and Minnesota [t4, t7]. While these lakes also form a vital internal waterway route for both nations (the St. Lawrence Seaway) and are central to the iron and steel industry, the specific 'imaginary line' described is the political demarcation defining Canada's southern limit in the Great Lakes basin [t2, t8, t9].

Sources

1. [1] https://www.noaa.gov/general-counsel/gc-international-section/great-lakes
2. [2] https://nauticalcharts.noaa.gov/publications/coast-pilot/files/cp6/CPB6_C03_WEB.pdf