How to Use a GPS Military Grid Reference System
Citizens of the world now rely on GPS navigation units to find their way about, but it doesn't have to be so. Some enjoy navigating the old-fashioned way--with map and compass. With a map utilizing the military grid reference system, you can find your precise point on a map, down to about 10 meters if you've got a landmark to work with. If you need to know which way to go from there, just use your compass pointed in a new direction to plan your trip around any obstacles.
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Instructions
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Locate the nearest major road or landmark to your position. Pinpoint it on your map. It may be less noteworthy, like a tall hill marked by concentric circles more concentrated than other nearby hills, or a steep valley, usually marked by concentrated concentric circles along a river.
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Find this point on your map and mark it with a pencil. Go right and up with your finger on the map to find first the letter, then the number for your grid identifier, which will be the location to the nearest kilometer on this map. For instance, go right to column G and up to row 5 to get 5G. (Read the legend for your particular map for sizing; detail will vary.)
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The next two letters in your MGRS point identifier will then identify the particular box your point is in. Find the two-letter box corresponding to your point. Again, go right and then up with the set of letters closest to the map. (On detailed maps, the letters and numbers you've used so far may not even be anywhere but on the label.)
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Find the next two numbers of your MGRS identifier by identifying the 100,000-square-meter box, usually identified with bold lines of longitude of latitude on your map. Go right, then up to find the two numbers corresponding to the lines of longitude and latitude of your point. They will be marked off every 100,000 meters. Write the two numbers down.
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The final two numbers will correspond to the 1,000-square-meter mark, which again you will get by going right and then up to get your final two designators. You can add another two or four numbers to the end of this by graphing 10 or 100 smaller increments of longitude and latitude within your 1,000-square-meter box. Continue downward to the nearest 10 meters if you've got the map and time--until you've pinpointed your location with an exact MGRS coordinate.
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Take out your compass. Draw a line on the map from your known location (you don't even need the number) to the point on the map where you want to go. Orient your map to north by lying your compass on top of it pointing due north. Keep your map facing this way to mirror the landscape around you.
Now align the compass along the line you've drawn on the map. Write down this angle, from 0 to 359 degrees. This will be your new direction of travel. Monitor your compass periodically so you don't drift off course. Measure your approximate distance by measuring off each kilometer box between you and your destination.
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References
Resources
- Photo Credit gps survey image by Brian Barrett from Fotolia.com
