latitude and longitude system uses angular measurements (degrees) to describe a position on the surface of the Earth. Lines of latitude, also known as parallels, run east-west across the globe (and maps), and as you might imagine, are parallel to each other – they do not cross, meet, or change in distance apart from one another. The best known line of latitude is the Equatoror 0°. The Equator makes a right (90°) angle with Earth’s axis of rotation (the imaginary line that runs through the poles about which the earth rotates). All lines of latitude represent the angle formed by the point on the surface, the center point of the Earth, and the closest point on the equator (Figs. 1, 2). Therefore, the numerical value for degrees of latitude increases moving away from the Equator in either direction, to a maximum of 90° at the poles. Lines of latitude measure distances north or south of the Equator. Because the Equator splits the Earth into two hemispheres(half spheres), we must always designate a direction – North or South (N or S), when indicating latitude. Everything north of the Equator is the northern hemisphere, while everything south is the southern hemisphere. Lines of longitudeare fundamentally different than lines of latitude. They are meridians(or half circles), which run north-south from pole to pole, across the globe (and maps). They are NOT parallel, but converge to a point at both poles. The best known line of longitude is the Prime Meridian, or 0°, which runs north-south through the Royal Observatory in Greenwich, England. Note, however, that since it is a meridian, it does not continue on the opposite side of the Earth. The opposing line of longitude (180°) closely corresponds to the International Dateline (which runs mostly through the Pacific Ocean and delineates one calendar day from the next).
. Figure 1 Comparison of latitude (parallels) and longitude (meridians) Figure 2: Earth's grid created by parallels and meridiansThe length of one degree of latitude on Earth (as measured along a meridian) is about 111 kilometers (or 69 miles). The width of a degree of longitude, however, varies depending on where the measurement is taking place. A degree of longitude at the Equator is 111 km, but 0 km at the North and South Poles. The distance between adjacent lines of
longitude gets shorter and shorter with proximity to the poles.