It's unknown exactly how many steps it is from the Datum, but we can deduce from the Mark Twain's journey that it is located between a world infested with large insects (Earth West 110,719) and Earth West 127,487.
The Long Earth
The Long War
In 2040, during the events of The Long War, Bill Chambers tells Joshua Valienté an apocryphal story of a comber who spent the night on the Cueball alone and naked, for a bet. In the morning, with a hangover, this alleged individual stepped North, and found himself on another planet, where, in the sky, he saw the Milky Way from the outside.