Q1. Q2. Q3. Q4. Q5. Q6. Q7. REVIEW  QUESTIONS Name the two coordinate systems used by the U.S.  military? On most charts, 60 nautical miles equals how many degrees of latitude? Convert 23.54N and 120.38W to tenths of a degree. When   you   use   the   Universal   Transverse Mercator  (UTM)  grid,  how  is  a  grid  zone identified? Grid zone 27R is between what latitude and longitude? What is normally the smallest grid zone used with the UTM grid system? The Universal Polar Stereographic (UPS) grid system is used in what region of the globe? AREAS OF THE GLOBE In meteorology and oceanography, several terms are used to describe sections of the world. Northern Hemisphere refers to the half of earth north of the equator; Southern Hemisphere refers to the area south of the equator.  Similarly,  Western  Hemisphere  refers  to the half of earth from the prime meridian westward to the international date line;  Eastern  Hemisphere  refers to the  half  from  the  prime  meridian  eastward  to  the international date line. You will see frequent references to the tropical region, or the Tropics. The Tropics is the belt surrounding earth that lies between the tropic of Cancer at 23½°N and the tropic of Capricorn at 23½°S. In meteorology, however, this region may generally be considered   the   belt   between   30°N   and   30°S. Geographically, the area of earth north of the Arctic Circle at 66½°N and south of the Antarctic Circle at 66½°S are the polar regions. Between the Tropics and each polar region lies the area referred to as the middle Figure 4-8.—Rhumb line and great circle tracks on a great circle chart (gnomonic projection). latitudes  (or  the  mid-latitudes).  Based  on  annual temperature changes, the Tropics, mid-latitudes, and polar regions are also respectively called the  Torrid Zone, the Temperate Zones, and the Frigid Zones. These terms are generally falling into disuse. CHART PROJECTIONS Several types of modifications to the shape of earth are made to allow the earth’s surface to be represented on flat paper charts and displays. These modifications are called "projections." The most common projections used  in  meteorology  and  oceanography  are  the Mercator projections, Polar Stereographic projections, and the Lambert-Conformal Conic projections, as shown in figure 4-7. Figure 4-7 also indicates the properties of these projections and their intended uses. You will often see references to great circle routes or tracks. A great circle track represents the shortest distance between two points on the surface of earth or on a globe, such as if a string were to be stretched between the two points. Great circle routes are planned on  a  special  chart  projection  called  a  gnomonic projection.  These  projections  are  similar  to  polar projections, except the plain of the chart is tangent to the earth at the center of the area charted. Figure 4-8 shows a gnomonic projection with a great circle route and a rhumb line track between two ports. The rhumb line track is a straight line drawn between two points on a Mercator projection, and may also be called a "Mercator track." Notice that the great circle route is about 800 nautical miles shorter than the rhumb line track due to the  curvature  of  the  earth.  Figure  4-9  shows  the identical routes drawn on a Mercator projection. CHART SCALE The scale of a chart refers to a comparison of the distances shown on a chart to the actual distance on the surface of earth. A scale may be a comparative ratio Figure 4-9.—Rhumb line and great circle course on a Mercator chart. 4-9