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Appendix D
Universal Transverse Mercator
coordinate system
The Universal Transverse Mercator (UTM) coordinate system uses two-dimensional Cartesian coordinates
to define locations on the surface of Earth. It is the preferred system for large scale mapping (1:250000
and larger scales), giving the advantage of simple numbers over the complex degrees, minutes and seconds
of latitude and longitude. For more details consult Terry Jr (1996).
As described in Hager et al. (1992) as well the Mercator Projection can be visualised as an ellipsoid projected
into a cylinder, tangent at the equator and the polar axis coinciding with the axis of the cylinder. Opening
and flattening the cylinder results in distortion at the polar regions, while the showing true distances along
the Equator.
The Transverse Mercator Projection is a Mercator Projection with the cylinder rotated by 90◦ , resulting
in the ellipsoid and cylinder being tangent along a meridian. In this case when the cylinder is flattened
the east and west extremities appear distorted, however there is no distortion along the meridian that is
tangent to the cylinder, showing true distances. The zone around the meridian considered still sufficiently
little distorted is 3◦ in each direction, resulting in 6◦ wide portions for the system, dividing the Earth in
60 longitudinal mapping zones. See also Hager et al. (1992).
Figure D.1: Illustration of the UTM. CM - Central Meridian; AB, DE - Lines of secancy formed by the
intersection of cylinder and ellipsoid. Image from Hager et al. (1992).
The Universal Mercator Projection modifies the cylinder of projection by reducing its elliptical dimensions
and making it secant to the ellipsoid. It results in intersecting the ellipsoid along lines parallel to the
central meridian. (See Figure D.1) In one 6◦ zone the lines of secancy establish approximately 180000 m
east and west from the central meridian. The effect of these lines of secancy is that of allowing a more
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