Transverse Mercator Projection

Transverse Mercator Projection

The transverse Mercator map projection is an adaptation of the standard Mercator projection. The transverse version is widely used in national and international mapping systems around the world, including the UTM. When paired with a suitable geodetic datum, the transverse Mercator delivers high accuracy in zones less than a few degrees in east-west extent.

The standard (or Normal) Mercator and the transverse Mercator are two different aspects of the same mathematical construction. Because of the common foundation, the transverse Mercator inherits many traits from the normal Mercator:

• Both projections are cylindrical: for the Normal Mercator, the axis of the cylinder coincides with the polar axis and the line of tangency with the equator. For the transverse Mercator, the axis of the cylinder lies in the equatorial plane, and the line of tangency is any chosen meridian, thereby designated the central meridian.
• Both projections may be modified to secant forms, which means the scale has been reduced so that the cylinder slices through the model globe.
• Both exist in spherical and ellipsoidal versions.
• Both projections are conformal, so that the point scale is independent of direction and local shapes are well preserved;
• Both projections have constant scale the line of tangency (the equator for the normal Mercator and the central meridian for the transverse).

Since the central meridian of the transverse Mercator can be chosen at will, it may be used to construct highly accurate maps (of narrow width) anywhere on the globe. The secant, ellipsoidal form of the transverse Mercator is the most widely applied of all projections for accurate large scale maps.