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A Quick Guide to Using UTM Coordinates
Standing at the road junction marked with the star on the topographic map pictured above, a GPS unit set to display position in UTM coordinates, would report a location of:
The 10 S represents the zone you are in. The zone is necessary to make the coordinates unique over the entire globe. The top set of numbers, 0559741, represent a measurement of East-West position, within the zone, in meters. It's called an easting. The bottom set of numbers, 4282182, represent a measurement of North-South position, within the zone, in meters. It's called a northing. The map has Universal Transverse Mercator (UTM) grid lines spaced every kilometer or 1000 meters. The vertical grid lines determine East-West position and the horizontal grid lines determine North-South position. Look along the bottom edge of the map at the labels for the vertical grid lines. 559 and 560000 mE. The label, 560000 mE., reads "five hundred and sixty thousand meters East." The label, 559, is an abbreviation for, 559000 mE. The two grid lines are 1000 meters apart. The horizontal grid lines are labeled in a similar manner.
If the metric system gives you heartburn, here are a few tips to help you out.
Shorthand for UTM Coordinates Most land navigation activities focus on a very small portion of the globe at any one time. Typically the area of interest to an outdoorsman is less than 20 miles on a side. This focus on a small area allows us to abbreviate UTM coordinates. The zone information and the digits representing 1,000,000m, and 100,000m are dropped. The 1m, 10m and 100m digits are used only to the extent of accuracy desired. A GPS unit might read
Using a notation similar to the one found on a USGS topographic map, this would be written as: Zone 10 S 559741 mE. 4282182 mN. An abbreviated format for the same coordinates would look like:
The 100m abbreviated format, 597 821, and the 10m abbreviated format, 5974 8218, are the most commonly used. Notice that the easting is reported first, followed by the northing. Remember the phrase "read right up" to help you remember to read the easting from left to right, followed by the northing from the bottom up. Also notice that when you abbreviate coordinates you should not do any rounding. 0559651 becomes 596 not 597. This ensures that your position is still within the reported square. As accuracy decreases, the square gets bigger.
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