Longitude lines converge from the equator toward the North and South poles. Thus the distance between longitude lines varies with latitude. Latitude lines always parallel each other. Longitude lines always lie in a true north and south direction, latitude lines always lie in a true east and west direction. However, much position fixing is done with magnetic compasses so it is necessary to understand the difference between true and magnetic north.
True north is based upon the rotation axis of the earth.
Magnetic north is the direction that a magnetic compass will point. Since the magnetic north pole is not located at the true North Pole, magnetic north readings must be corrected. Charts come with compass roses on them that show the relationship between true and magnetic north. This difference will be important in our work since we will be taking magnetic compass readings to position ourselves relative to true north. In coastal waters you can determine your position by taking bearings off of landmarks using a compass.