As was pointed out it is all relative. In general, it is more common to hear within spitting distance to mean pretty close (measured in feet, not miles).
As wrholt pointed out, it is really just relative to how the person feels about it. My family all say I live next to the ocean. In that case "next" is 10 miles away. To them it is next to the ocean since they lives hundreds of miles away. Of course no one in Tampa would say I live "next" to the ocean.
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