In a rather bizarre Wikipedia discussion about the flatness of Earth, I found an interesting statement:
– At the scale of less than 10^-9 meters or so, the earth is a space has an undefinable shape.
– From about 10^-9 meters through to about 10^4 meters, the earth is flat.
– From about 10^4 meters to about 10^9 meters the earth is a sphere.
– At the scale of anything greater than about 10^9 meters, the earth is a point.
I guess the morale is that everything is relative.