MART Vol. II MO/MP - NESA - Civil Air Patrol

There is no natural starting point for numbering longitude, so the solution is toselect an arbitrary starting point. When the sailors of England began to makecharts, they chose the meridian through their principal observatory in Greenwich,England, as the zero line. Most countries of the world have now adopted this line.The Greenwich meridian is sometimes called the first or prime meridian (actually,the zero meridian).Longitude is counted east and west from this meridian through 180º. Thusthe Greenwich Meridian is zero degrees longitude on one side of the earth, andafter crossing the poles it becomes the 180th meridian (180º east or west of the 0-degree meridian). Therefore we have all longitudes designated either west oreast, for example, E 140º or W 90º. The E and W designations define the easternand western hemispheres.5.2.3 Position locationRefer to Figure 5-1. By convention, latitude is always stated first.Figure 5-1This system is used to precisely locate any point on the earth's surface.When identifying a location by its position within this latitude-longitude matrix, youidentify the position's coordinates, always indicating latitude first and thenlongitude. For example, the coordinates N 39° 04.1', W 95° 37.3' are read as“north thirty-nine degrees, four point one minutes latitude, west ninety-fivedegrees, thirty-seven point three minutes longitude.” If you locate thesecoordinates on any appropriate aeronautical chart of North America, you willalways find Philip Billard Municipal Airport in Topeka, Kansas.It is important to remember that in the northern hemisphere, latitude numbersincrease as you proceed from south to north (more north), and decrease as youmove north to south (less north). In the western hemisphere, longitude numbersincrease when proceeding east to west (more west), and decrease when movingwest to east (less west). Since the GPS receiver displays latitude and longitudewith a great degree of accurately, pilots can use this tool to navigate and to flyvery precise search patterns.70