[narcindin]

Looks like the 2020 line is just east of Chicago and just north of the SFBA.

The line can't move West or South too quickly as every additional minute represents so many people shifting from one side of the median to the other.

[Retric]

Not just movement east west or north south but also births, deaths, immigration, and emigration.

Also of note, the quadrants aren’t balanced. You could have 1x in the northwest, 2x in the northeast, 2x in the southwest, and 1x in the southeast.