Transverse Mercator projection

The transverse Mercator map projection (TM, TMP) 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 Universal Transverse Mercator. When paired with a suitable geodetic datum, the transverse Mercator delivers high accuracy in zones less than a few degrees in east-west extent.

Standard and transverse aspects

The transverse Mercator projection is the transverse aspect of the standard (or Normal) Mercator projection. They share the same underlying mathematical construction and consequently 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 on 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.