Reader Question: Fixing Position

Illustration Terrain to Map

Pete, the best way to keep this straight is as follows. When working with terrain use magnetic azimuth and when working with a map use grid azimuth.

Take a look at the illustration above. Let’s assume that you are working a ridgeline. You I.D. a position that you want to fix on your map.

Step 1. Using your compass shoot three bearing lines (magnetic azimuth). Note that where the three lines cross a triangle is formed. Record the magnetic azimuth in your notebook.

Step 2. Let’s now plot the target on a grid map. Convert each magnetic azimuth to grid azimuth. Why? You are going from terrain to map.

Step 3. Using your protractor, plot each grid azimuth line. Where those lines intersect a triangle will be formed. Place a dot in the center of the triangle and determine the grid coordinates of that point.

You have now successfully gone from terrain to map.

Now, let’s assume that you are going from map to terrain and the triangle, or desired objective,  is a rally point. To get there, you must navigate using your compass. So what do you do.

Step 1. Determine the grid azimuth to the rally point (from your location) using your protractor. Keep in mind that your desired objective will likely be out of your line of sight, and possibly 3 or 4 kilometers from you.

Step 2. Convert the grid azimuth to magnetic azimuth.

Step 3. Determine range to the rally point.

Step 4. With magnetic azimuth and range determined use your compass and beads to get to your desired location.

You’ve now gone from map to terrain so you are working with magnetic azimuth.

It takes practice, plan on being disoriented but you’ll get there. Hope this helps you.

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