The 45th parallel north is often called the halfway point between the Equator and the North Pole, but the true halfway point is actually 16.2 kilometers (10.1 miles) north of the 45th parallel because the Earth is oblate, that is, it bulges at the equator and is flattened at the poles.

In Michigan, the Old Mission Peninsula in Grand Traverse Bay ends just shy of the 45th parallel. Many guidebooks and signs at the Mission Point Lighthouse describe it as being halfway between the equator and north pole. When the Grand Traverse Bay recedes below normal level, it is possible to walk out to the exact line.