A grid system is a set of lines that cross each other at right angles on a map. Grid systems allow the map user to locate or report on a specific point on the map. For example, longitude and latitude lines on a Mercator-projection map form a rectangular grid system that can be used to identify locations. Another grid system that is widely used in mapping and orienteering is the Universal Transverse Mercator or UTM Grid system. Why do you think the word Mercator is used in the name of the system? The Military Grid Reference System is a military version of the civilian-use UTM system.

Hands on Activity

Activity: What other kinds of grid systems are there? Do a search on the Internet or in the library to find out.

Universal Transverse Mercator or UTM Grid

An easier-to-use grid system for specifying a point on a topographic map is the Universal Transverse Mercator or UTM Grid. This grid system subdivides the map region into one kilometre squares. Each marked UTM line on the map is exactly 1000 metres (1 kilometre) to distance from a reference point. Points that fall between the marked UTM grid lines can be accurately located by using the 1000 metre scale bar found at the bottom of the map.

Reading UTM Coordinates on a Topographic Map

UTM lines are marked on the margins of United States Geological Survey, or USGS, topographic quadrangle maps as small, blue tick marks with numbers beside them. The upper-left and lower-right corners of the map show the full UTM coordinates. These numbers are read simply as numbers of metres east or north of a reference line. The digits are printed at different sizes to accentuate the thousands and ten thousands places, which change as each new grid line marks 1000 metres of distance. Notice that the ones, tenths, and hundredths places are left off of most of the UTM coordinates printed on the map.

Military Grid Reference System

The military grid reference system is very similar to the civilian UTM system, but avoids UTM's cumbersome long strings of numbers by using a rectangular grid with, on 1:500,000 scale and larger maps, two digit numbered rows and columns. Military grid references are very similar to the mathematical Cartesian (x,y) system. Military grid coordinates first give eastings on the x axis, and then northings, on the y axis.

Reading Military Grid Reference Coordinates

In this example, the designation of the square containing the school would be 67E42N. This is called a four-figure grid reference. In order to give a more precise military grid reference, you must imagine the square divided into ten sections by ten sections. The grid reference will then be an estimate of that internal ten by ten division of a grid square. We can estimate that the school is six tenths of the way "east" from the western boundary of the grid square, line 67. Horizontally, we can estimate also that the school is approximately five tenths of the way up from the southern boundary of the grid square, line 42. We can then give a six-figure grid reference for the school of 676E425N.