The 45th Parallel is an invisible mapping line halfway between the Equator and the North Pole, part of a latitude and longitude system dating back to 200 B.C. and the Greek astronomer Hipparchus. For over two thousand years it has played a key role in navigating the earth, first for seafarers crossing the ocean with only the sun and stars to guide them. Today, even with global technologies able to pinpoint location on earth to within 12 inches, it remains a valuable way to connect places around the planet, linking locations such as the prairies of South Dakota, the north woods of Maine, the wine country of France, and the deserts of Mongolia. As understanding of the earth improved, the line was corrected to shift slightly north 10 miles after discovery that the earth's rotation caused a bulge at the equator.