The boundary between the United States and Canada, including the portion adjacent to Alaska, is probably the longest international boundary in the world common to two countries, as it has a total length of 5,527 miles-- 1,789 miles land boundary and 2,198 miles water boundary from Passamaquoddy Bay to the Pacific Ocean and 1,540 miles from the southernmost point of Alaska to the Arctic Ocean.
This boundary is defined in a variety of ways. It follows minor streams, it winds between the islands of such waterways as the St. Lawrence River, it traverses open bodies of water, such as the Great Lakes, it runs along the winding crest of a watershed for three long stretches, it is fixed by two parallels of latitude and one meridian of longitude, and in southeastern Alaska it is defined by a line running between mountain summits.
A line of such length and diversity of definition necessarily presents widely differing topographic and social features. The land boundaries run along land in cultivation, through dense forests where the growth is rapid owing to the high precipitation, across the rolling and treeless plains, through swamps, and over the slopes and summits of mountains covered with perpetual snow. The water boundaries range from well-defined arteries of commerce to trickling streams visited only by the trapper or sportsman. In places the boundary is near towns and cities, but for long stretches, particularly in Alaska, it is far removed from human habitation and bases for supplies.