Finding Your Location by Resection, Land Nav 101

Our previous articles in the last week or so have centered upon getting back to the basics of land navigation. It is imperative that all of these skills and they are the basics of finding your way in the field, become second nature to all of the candidates who aspire to be in the Special […]

The Land Navigation course for SFAS also known as the Star Course in Hoffman, NC outside of Camp Mackall is the toughest individual land navigation course you will find in the U.S. military. You’ll be traveling several kilometers between points and the terrain is filled with thickets, swamps and low-level terrain where a hilltop on the map may look more like an anthill on the ground.

That’s why it is imperative for all of the candidates to learn the basics of land navigation to the point where you could teach a class on any of it, keep a cool head and prepare. As we’ve said here many times, land navigation requires as much prep and practice as any other perishable skill.

But also remember, that you’ll be only asked to pass the same course that thousands of other candidates have passed before you. Although difficult, it is far from impossible. Don’t let the countless stories, usually perpetuated by those who failed the course, fill your heads with needless worry. Ignore the noise. Especially from those who didn’t get selected. Prepare to succeed, and you will.

So, today we’ll tackle a common issue for many candidates that find themselves on the land navigation course. This is the way of finding your exact location if you are unsure of your exact map placement.

The military definition of Resection for finding your exact location on a map by determining the grid azimuth to at two or more well-defined locations that can be pinpointed on the map. For greater accuracy, the desired method of resection would be to use three or more well-defined locations.

In layman’s terms, if you aren’t sure exactly where you are at and need to pinpoint your location and can see two or more distant points that are recognizable on your map sheet, you can shoot an azimuth to them and determine the back azimuth from those points to pinpoint your location.

For the purposes of doing it correctly you’ll need at least two known points but obviously, three or more is ideal. There are three methods of using resection, using the map and compass method, the straightedge method and the modified method. In a perfect world, the map and compass method is the way to go. But in reality, you’ll often in the real world use the modified Resection method, as often times, you may not have the luxury of having multiple points visible.

Map and Compass Method

Orient the map using your compass and terrain association
Identify two or three known distant locations on the ground and mark them on the map accordingly.
Measure the magnetic azimuth to the first of the known positions from your location using a compass.
Convert the magnetic azimuth to a grid azimuth using the declination diagram.
Convert the grid azimuth to a back azimuth. If the magnetic azimuth is less than 180 degrees add 180. If the azimuth is more than 180 degrees subtract 180.
Using a protractor, draw a line for the back azimuth on the map from the known position back toward your unknown position.
Repeat the same steps for a second position and a third position, if practical.

Where all of the lines intersect on your map is your location. Next, using your protractor, determine the grid coordinates to the desired accuracy, an eight-digit grid being the preferred accuracy for our purposes. You’ve found your location. Easy, peasy…right?

Straightedge Method:

This method is a little bit differently but can still accurately find your position. To do so the successful navigator must follow these steps:

Orient his map using his compass and/or terrain association
Locate at least two known distant locations or prominent features on the ground and mark them on the map accordingly.
Lay a straightedge on the map, in this case using the edge of the compass and a known position as a pivot point.
Rotate the straightedge until the known position on the map is aligned with the known position on the ground.
Draw a line along the straightedge away from the known position on the ground toward your position.
Repeat the same process using a second known position that you can see from your location.

This one sounds more difficult than what it truly is. However, where the intersection of the lines meet on the map is your location. Determine the grid coordinates to the desired accuracy. You then should be able to get an eight-digit grid coordinate and find your way to your point.

Modified Resection Method:

The modified method is the least preferred and the least accurate method but is useful in certain situations. If you’re not certain of your exact location but are located on a linear terrain feature such as a road, creek or along a similar body of water, this can pinpoint your position.

Orient the map using a compass and/or by terrain association.
Locate a point in the distance that can be easily identified on the ground and on the map.
Determine the magnetic azimuth from your location to the distant known point.
Convert the magnetic azimuth to a grid azimuth.
Convert the grid azimuth to a back azimuth, using the add or subtract 180 accordingly depending on the degrees.
Using a protractor, draw a line for the back azimuth on the map from the known position back toward your unknown position.

Your location is where the line on the map crosses the linear feature. Determine the grid coordinates to the desired accuracy, for our purposes an eight-digit grid coordinate. In a practical application, if you have to cross a thick draw or swampy area and are closing in on your point but aren’t sure of where you are after negotiating the thicket, do the steps outlined above. After identifying a far point, this will closely put you to where you are and then you can finalize your attack point and find your way.

You’ll find this little exercise a very helpful method anytime you are navigating your way in the field and aren’t entirely sure of where you are. Remember, any of these exercises that you aren’t entirely sure of conducting properly can be done with any map, compass, and protractor. Practice makes perfect. Slow is smooth and smooth is fast.

Photos courtesy of Army Study Guide, author, DOD