"Thus certain bombs were designed to destroy an entire large city even if dropped five to ten kilometers from its center. This objective meant that yield and effectiveness were positively correlated, at least up to a point. However, the advent of ICBMs accurate to 500 meters or better made such yields unnecessary. Subsequent nuclear weapon design in the 1960s and 1970s focused primarily on increased accuracy, miniaturization, and safety. The standard practice for many years has been to employ multiple smaller warheads (MIRVs) to «carpet» an area, resulting in greater ground damage."
So sprawling won't save you neither from the initial "nuclear carpet" (that can be quite wide), nor from the radioactive fallout that have always spread over a much larger area than the radius of initial explosion(s).
http://en.wikipedia.org/wiki/Tsar_Bomba
"Thus certain bombs were designed to destroy an entire large city even if dropped five to ten kilometers from its center. This objective meant that yield and effectiveness were positively correlated, at least up to a point. However, the advent of ICBMs accurate to 500 meters or better made such yields unnecessary. Subsequent nuclear weapon design in the 1960s and 1970s focused primarily on increased accuracy, miniaturization, and safety. The standard practice for many years has been to employ multiple smaller warheads (MIRVs) to «carpet» an area, resulting in greater ground damage."
So sprawling won't save you neither from the initial "nuclear carpet" (that can be quite wide), nor from the radioactive fallout that have always spread over a much larger area than the radius of initial explosion(s).