well one mathematician says curvature is 8 inches

well one mathematician says curvature is 8 inches /mile which is only 4666 ft over 7000 miles- no reason to go thousands of miles N- what are we missing? what that misses is just the lessor circumference towards the poles

whatever it is they dont save that many miles-when I draw a string on a globe both ways along the great circle path I get a mileage savings of only 2.3%-not scientific -just saying-so a recreational vehicle wouldnt want to do this-other things would be more important