18 A globally accepted system that uses latitude and longitude coordinates allows us to locate any place on the earth’s surface. Latitude measures locations on the globe that are north and south of the Equator. The measurements are stated in degrees, minutes and seconds. The highest numerical readings for latitude are ninety degrees North (90°N) and ninety degrees South (90° S). The Equator is zero degrees (0°). The Equator divides maps of the earth into Northern and Southern hemispheres. When lines of latitude are shown on a map, a globe or a graphic of the earth, they are displayed as parallel lines with the Equator and they are equidistant. One degree of Latitude is equivalent to 69 miles. There are small variations at the Equator and the Poles. The variations have been calculated and are used when required. Longitude measures locations east and west of the Prime Meridian. In 1884 it was agreed that the Prime Meridian identified a location in Greenwich, London, England. You should note that the more widely used meridian in more modern times is the IERS Reference Meridian. The International Reference Meridian (IERS) was devised from the Greenwich Meridian but it is slightly different. The difference between both exists because of variations between astronomical Continues on next page
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