Developed by the military, the UTM grid (Universal Transverse Mercator grid) has the advantage of being able to depict most places on the globe as true rectangles or squares.
Who in the World Was Gerard Mercator?
In a nutshell, Gerard Mercator was a 16th-century Flemish geographer who developed a method of projecting the round globe onto a flat surface—a trick akin, I suppose, to painting a picture on a basketball, then cutting the basketball open and laying it flat to frame the picture.
You’ve probably seen the familiar flat Mercator’s map of the globe. It has the advantage of accurately depicting on paper the same angles and shapes as those occurring on this spherical planet, which in and of itself is a pretty cool trick.
There is, however, just one little problem. (You knew there had to be.) Mercator’s projection is fairly accurate near the Equator, but toward the poles, the size distortion is great. Greenland, for instance, on a Mercator’s map looks as large as South America. In truth, South America is eight times larger than Greenland.
Developing the Grid
Needing maps that could depict with a high degree of accuracy areas of the round earth using a grid composed of flat rectangles, the U.S. Army took Mercator’s projection, turned it sideways, and ended up with what they needed.
Since a sideways projection is called a “transverse” projection, and since the Army used a sideways Mercator projection, the resulting grid is called the Universal Transverse Mercator grid. Based on the metric system, it covers the globe from 80° south latitude to 84° north latitude with little distortion.
Since distortion would be too great at the poles, however, these areas are covered using another grid—the Universal Polar Stereographic (UPS) grid. If you plan to mush to the North Pole, or count penguins in Antarctica, you need to read up on the UPS grid before hitching up your sled dogs at either frozen end of the globe.
How the UTM Grid Works
To help you understand how the UTM grid works, I have created a special web page entitled, well, How the UTM Grid Works.
In addition, below you'll see a half-hour video I made explaining the grid.
My suggestion is that you review both of these to get a more complete understanding of the topic.