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Understanding Map Projections

Understanding Map Projections

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TWO-POINT EQUIDISTANT<br />

point represents the correct great circle length but<br />

not the correct great circle path.<br />

LIMITATIONS<br />

Does not represent great circle paths.<br />

USES AND APPLICATIONS<br />

Used by the National Geographic Society for maps of<br />

Asia.<br />

The first point is 117°30' W, 34° N, and the second point is<br />

83° W, 40° N.<br />

Adapted form used by Bell Telephone system for<br />

determining the distance used to calculate long<br />

distance telephone rates.<br />

DESCRIPTION<br />

This projection shows the true distance from either<br />

of two chosen points to any other point on a map.<br />

PROJECTION METHOD<br />

Modified planar.<br />

POINTS OF CONTACT<br />

None.<br />

LINEAR GRATICULES<br />

Normally none.<br />

PROPERTIES<br />

Shape<br />

Minimal distortion in the region of the two chosen<br />

points, if they’re within 45 degrees of each other.<br />

Increasing distortion beyond this region.<br />

Area<br />

Minimal distortion in the region of the two chosen<br />

points, if they’re within 45 degrees of each other.<br />

Increasing distortion beyond this region.<br />

Direction<br />

Varying distortion.<br />

Distance<br />

Correct from either of two chosen points to any<br />

other point on the map. Straight line from either<br />

Supported map projections• 91

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