The Longest Borders Between Two Countries

The border between Canada and the United States is the longest international boundary in the world: 8,891 km, including the 2,475 km stretch between Alaska and Canada. Much of it is the straight line of the 49th parallel, surveyed in the 19th century and marked by a cleared strip of forest six metres wide that runs for thousands of kilometres.

The ten longest

1. Canada – United States: 8,891 km.
2. Kazakhstan – Russia: 7,644 km, the longest continuous land border (no sea sections).
3. Argentina – Chile: 5,308 km, running the length of the Andes.
4. China – Mongolia: 4,630 km.
5. China – Russia: 4,133 km, in two sections east and west of Mongolia.
6. Democratic Republic of the Congo – Angola: 2,646 km.
7. China – India: about 3,380 km, much of it disputed and unmarked.
8. Mongolia – Russia: 3,452 km.
9. Brazil – Bolivia: 3,403 km.
10. India – Bangladesh: 4,142 km, the longest border India shares with any neighbour and one of the most heavily fenced.

Figures vary between sources because of disputed sections and the coastline-style difficulty of measuring a wiggling river boundary. The ranking of the top few, though, is stable.

The shortest borders

At the other extreme, the border between Spain and Gibraltar is about 1.2 km; between Zambia and Botswana it is roughly 150 metres at a single point on the Zambezi; and the border of the Vatican with Italy is 3.4 km around a walled enclave in Rome. Botswana and Zambia's near-point meeting is so short that whether the two countries actually share a border at all was legally argued for decades.

Borders that are just lines

Many of the longest borders follow lines of latitude or longitude rather than rivers or mountains, a legacy of colonial and treaty map-drawing: the US–Canada 49th parallel, the Egypt–Sudan and Egypt–Libya borders, the Namibia–Botswana and Namibia–Angola borders, and much of the Sahara. Straight borders tend to mean the boundary was drawn by outsiders far from the ground.