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On a Mercator chart, the distance of 1-inch measured at Equator corresponds to 25 NM. Calculate the scale at 43°N latitude.
  • A
    1 : 50 000
  • B
    1 : 500 000
  • C
    1 : 1 000 000
  • D
    1 : 1 333 000

1 inch = 2.54 cm
25 NM = 4630000 cm = 1 822 835 inches

Scale at Equator = Chart length / Earth distance = 1 / 1 822 835

On a Mercator chart:
Scale denominator A x cos (Latitude B) = Scale denominator B x cos (Latitude A)

1 822 835 cos (43°) = Scale denominator B cos (0°)
Scale denominator B = 1 333 137

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