A particular subset of the transverse Mercator is the
Universal Transverse Mercator (UTM) which was adopted
by the US Army for large-scale military maps. Here, the
globe is divided into 60 zones between 84S and
84N, most of which are 6 wide. Each of
these UTM zones have their unique central meridian.
**GMT** implements both the transverse Mercator and the
UTM projection. When selecting UTM you must specify:

- UTM zone (1-60). Use negative value for zones in the southern hemisphere
- Scale along the equator in inch/degree or 1:xxxxx (
**-Ju**), or map width (**-JU**)

In order to minimize the distortion in any given zone,
a scale factor of 0.9996 has been factored into the formulae.
(allthough a standard, you can change this with **MAP_SCALE_FACTOR**).
This makes the UTM projection a *secant* projection and not
a *tangent* projection like the transverse Mercator above.
The scale only varies by 1 part in 1,000 from true scale at
equator. The ellipsoidal projection expressions are accurate for map areas
that extend less than 10 away from the central meridian. For
larger regions we use the conformal latitude in the general spherical
formulae instead.