double meridian distance—The sum of the meridian distances of the ends of a survey line. In practice, assuming a closed traverse with the meridian of reference passing through the initial station, the double meridian distance (DMD) of the first course (line) is equal to the departure of that course; the double meridian distance of each succeeding course (line) is equal to the double meridian distance of the preceding course, plus the departure of the preceding course, plus the departure of the course itself. If the DMD of each course is multiplied by the latitude of the corresponding course, double areas are obtained, from which the area of the tract can be obtained. By a strictly analogous procedure, double parallel distances (DPD) can be computed, using the latitudes of the successive courses instead of departures, and using an east-west line as the reference parallel.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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