Meridional Parts (or Increased Latitude): It is the length of the arc of meridian in the Mercator projection, comprised between the Equator and the considered latitude and expressed in minutes of Equator. Noted with (ϕc) or (M).
The fundamental theoretical problem of the Mercator projection:
The problem of accurate determining of the distance from the Equator to a parallel of any latitude, so that the condition of compliance is met.
To maintain the correct proportions between degrees of latitude and degrees of longitude, the degrees of latitude must be progressively longer as the distance from the Equator increases.
The meridional-parts correspond to the length of the small portions of the meridian that have suffered deformations in the Mercator projection.
The length of a meridian, increased between the Equator and any given latitude, expressed in minutes of arc at the Equator as a unit, constitutes the number of meridional parts corresponding to that latitude.
Meridional-parts make it possible to construct a Mercator chart and to solve problems in Mercator sailing.
The method of dividing the meridian into an increased latitude was developed by Eduard Wright in 1645.
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