Datum Madison refers to the city of Madison, Wisconsin on Datum Earth.
The Long Earth[]
In 2030, Humanity First detonated a nuke, destroying the city.[1]
The Long War[]
In 2040, after the Madison bombing, nobody was allowed to stay too long in the city because of the radiation.[2] The place was called "America's Chernobyl" by some and prairie flowers grew on flash-burned rubble.