TLDR: the county just picks a default direction, like “1 is East,” and then runs with it.
In the USA, there is no single authority that makes this decision nationwide, but in 1863, the US Postal Service let it be known that everyone had better figure it out or they wouldn’t get prompt mail service. So most states passed laws setting up a default system, with exceptions if towns had a good reason for it.
West of the Appalachians, this system tends to be extremely regular. Here are the laws for Macon county, Illinois:
https://codelibrary.amlegal.com/codes/maconcounty/latest/maconcounty_il/0-0-0-1330
And an explainer for rural Iowa:
https://iowahighways.org/highways/countyrd.html
But in West Virginia, things can get really weird, because some people don’t want to have numbers on their house:
https://www.theatlantic.com/magazine/archive/2013/01/where-the-streets-have-no-name/309186/
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