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In a polar stereographic chart for the northern hemisphere the true course of a straight line at latitude 60°N and longitude 170°W is 315°.

Calculate the true course of the straight line at longitude 145°E.The true course is:

  • A
    270°.
  • B
    354°.
  • C
    315°.
  • D
    276°.

In a Stereographic chart a a great circle is almost a straight line and we know that chart convergence is the angle of inclination between meridians on the chart, (or the change in direction of a straight line), between 2 longitudes.

Chart convergence for a stereographic chart is correct at the Poles and constant across the chart:

Chart convergency = Change in Longitude
Chart convergency = 45º

The change in direction of the straight line will give us chart convergence, with reference to the D-I-I-D scheme, flying westerly in the Northern Hemisphere, the angular value of the GCT will decrease:

GCT at B = 315º - 45º = 270º

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