What Is Grid Convergence?

Written by cee donohue
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What Is Grid Convergence?
Grid convergence plays a part in measuring the Earth. (3d earth image by Zoltán Pataki from Fotolia.com)

Grid convergence is a point in the Universal Transverse Mercator (UTM) system. The UTM system is a method of specifying locations on the Earth's surface. It was designed by the United States Army Corp of Engineers. It is a grid-based, mathematical system which approximates the Earth's truest size and shape.


Grid convergence is the horizontal angle measured from true north to grid north. True north and grid north are the same along the central meridian of the UTM grid zone. Outside of the central meridian, true north departs from grid north due to the convergence of the meridians.


Depending on your location, grid convergence will vary. If you are in the northern hemisphere, grid convergence is negative east and positive west of the central meridian. If you are in the southern hemisphere, grid convergence is positive east and negative west of the central meridian.


Grid convergence within the UTM system is a function of both latitude and longitude. The UTM system is the most used system in measuring the Earth's surface due to its precision.

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