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Mapping the Earth

Mapping the Earth. Geographic Coordinate System. Latitude & Longitude. Degrees, Minutes, Seconds or Decimal Degrees. Universal Time. Projected Coordinates. Why Project a Map?. Types of Projections. Projection Issues. Geographic Coordinates. Latitude and Longitude.

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Mapping the Earth

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  1. Mapping the Earth Geographic Coordinate System Latitude & Longitude Degrees, Minutes, Seconds or Decimal Degrees Universal Time Projected Coordinates Why Project a Map? Types of Projections Projection Issues

  2. Geographic Coordinates Latitude and Longitude • Reference Grid – covers the entire planet • Latitude (Parallels) – measured from the Equator (0º) • North or South • Never intersect • Longitude (Meridians) – measured from Prime Meridian (0º) • East or West • Intersect at the Poles

  3. Latitude Referenced to the North or South North Pole – 90º N Arctic Circle – 66º33’38” N Tropic of Cancer – 23º26’22”N Equator – Reference Line Tropic of Capricorn – 23º26’22”S Antarctic Circle – 66º33’38”S South Pole – 90º S

  4. Longitude Referenced to the East or West Prime Meridian 0º 180th Meridian 180º International Date Line

  5. Measuring Latitude & Longitude Degrees, Minutes, Seconds • A Circle can be broken into 360 Degrees (think of a compass) • Each Degree is made up of 60 Minutes (of arc) • Each Minute is made up of 60 Seconds (of arc) • Greater Accuracy of Measurements Decimal Degrees • Mathematical conversion of Degrees, Minutes, Seconds • Decimal portion is equal to: • (Minutes/60) + (Seconds/3600) • Example: 23º 26’ 22” N • 26/60=.43333 • 22/3600=.00722 • 23.44055º N

  6. Time on the Earth Time Zones • The Earth is split into 24 Time Zones • Time Zones are delineated around existing features International Date Line • Roughly the 180th Meridian • Gain a day traveling West across the line Universal Time • Based on the time at the Prime Meridian • Continuation of old Greenwich Mean Time (Zulu Time) • Standardized time across the world

  7. Projections Why Project? • The Earth is Round – Maps are Flat • No matter what is done, there will be error in a map • Projections attempt to minimize the error • Three kinds of error • Scale (Size) • Direction • Area • No Map can eliminate all error – must find the best balance • Depends on use

  8. Projections Basic Classes • Cylindrical • Conical • Azimuthal • Cylindrical – Generally large, rectangular areas • Conical – Medium sized, triangular areas • Azimuthal – Small, circular areas

  9. Projections Mercator • Common Projection • Good for navigation • Latitude/Longitude are all right angles • Shapes are correct but size is distorted at the poles

  10. Projections Robinson • Becoming more widespread • Minimizes error – no point is free of error • Low distortion within 45 Degrees of center • More realistic view of the entire world

  11. Projections Albers Equal-Area Conic • Common projection for the United States (Lower 48) • Maintains proper sizes • Shape errors increase away from center

  12. Projections Airy • Azimuthal projection (circular area) • Minimum-error projection • Does not fully eliminate errors

  13. Projections Projection Errors • Tissot Indicatrix • French Cartographer • Shows error in relative size and shape Mercator Robinson Albers Airy

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