It would be interesting to see the source and methodology. I suspect a lot more out-of-state people drive through Rhode Island or Delaware (and even stop to see a sight or two) than say South Dakota or North Dakota, but they do not stop overnight because RI and Delaware are so small.
24 million a year in North Dakota? If it's by hotel stays per night I would think all the energy industry workers are skewing that statistic. Maine, for one, also gets an incredible amount of air b&b and cottage rentals that hold a lot of people at a time and never sign a guest log or pay a hotel tax.
That's a great point! Maybe the campers and hikers are not counted in since they basically only count in the hotel/motel/hostel/b&b visitors? Most of the campers wouldn't use hotel etc. I'd guess, so they won t be seen in the statistics.