Map

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Map
a model or representation of the Earths surface
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Eratosthenes

• Greek mathematician who calculated the Earths
  circumference in 240 BC

• Using geometry and observation, his observations
  made more than 2,000 years ago were off by 6250
  km gt only 15!

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Finding direction on the Earth

• a fixed place on the Earths surface from which
  direction and location can be described

Reference point
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Axis

• an imaginary line through the earth about which
  the planet rotates

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North Pole

• north end of the axis

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South Pole

• south end of the axis

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Cardinal directions

• north, south, east, west and various combinations
  of these directions

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North on top

• is arbitrary

• Europeans placed east on top to show the
  importance of Jerusalem to their faith

• Chinese placed south on top as nothing of
  interest to them was to the north

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Compass

• uses the natural magnetism of the Earth to
  indicate direction

• compass needle points to the magnetic north pole

• the Earth has 2 different sets of poles gt
  geographic poles and magnetic poles

• magnetic poles have a slightly different location
  than the geographic poles

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Chinese Compass 220 BCE
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True North and Magnetic Declination
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True North

• geographic North Pole

• never changes position

• the difference between magnetic north and true
  north (geographic north pole) requires a
  calculation

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Magnetic Declination

• is measured in degrees east or west of true north

• has been determined for different points on the
  earths surface

• when the declination of an area is known, a
  compass can be used to determine true north

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