__Ellipsoid__

__Ellipsoid__

is the name of the volume obtained when an ellipse is rotated about one of its axes. Specifically, an oblate spheroid is an ellipse rotated about the shorter (semi-minor) axis. The Earth is not an exact ellipsoid, and deviations from this shape are continually evaluated. the curvature of the Earth’s surface is not uniform due to irregularities in the gravity field

__Geodetic Datum__

__Geodetic Datum__

is a definition of a model for the surface of the earth. They usually consist of the definition of an ellipsoid, a definition of how the ellipsoid is oriented to the earth’s surface, a definition for the unit of length, an official name, and region(s) of the earth’s surface for which the datum is intended to be used.

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__Map Projection__

__Map Projection__

A map projection is a mathematical formula which has been designed to convert the latitude/longitude method of positioning on the surface of a sphere into another method of positioning which can be plotted onto a flat map with some degree of controlled error and known accuracy. ( X Y Cartesian) coordinates. The most commonly used map projection is 1- the Transverse Mercator (TM) 2- the Universal Transverse Mercator (UTM) 3- The Lambert map projection

__Convergence__

__Convergence__

is the difference between Grid North and True North (Figure 3-3). Clearly, at the central meridian, Grid North equals True North. Convergence will vary with distance away from the central meridian and with distance away from the equator. Convergence is negative to the East and positive to the West.

** Grid north:** Is a navigational term referring to the direction northwards along the grid lines of a map projection. It is contrasted with

** True north:** Is the direction of the North Pole.

** Magnetic north: **Is the direction in which a compass needle points.

__Lambert Projection:__

__Lambert Projection:__

In cartography, the Lambert cylindrical equal-area projection, or Lambert cylindrical projection, is a cylindrical equal-area projection. This projection is undistorted along the equator, which is its standard parallel, but distortion increases rapidly towards the poles. Like any cylindrical projection, it stretches parallels increasingly away from the equator. The poles accrue infinite distortion, becoming lines instead of points.