The U.S. and Canada may be as lovey-dovey as two neighbors can get, but according to this charming video history by CGP Grey, both countries agreed to tuck themselves a little bit in, 10 feet back for America, 10 feet back for Canada, creating a corridor of open, surveillable, clear space between them.
This ribbon of emptiness is constantly monitored, regularly gardened (Baby Tree! Be gone!) and persists for 5,500 continuous miles — considered the longest deforested straight line in the world — protecting the U.S. and Canada from interlopers, or beavers without passports.
Except for one thing — it isn't straight.
The engineers who tried to follow the 49th parallel used primitive instruments, and, it appears, twine, and so the border got a wee bit zigzaggy, producing a number of problems, a few of which are delightfully described here ...