Just how they are constructed is a difficult mathematical affair but, roughly, the idea of their construction is based upon the earth being a cylinder, instead of a sphere.
"Lectures in Navigation"
Ernest Gallaudet Draper
I reached my goal when the sun was twelve degrees above the horizon, and was therefore better able to mark a mathematical position than Mr. Peary could have with the sun at less than seven degrees.
"My Attainment of the Pole"
Frederick A. Cook
I had made the admission that I was uncertain as to having reached the exact mathematical Pole.
"My Attainment of the Pole"
Frederick A. Cook