How to Use a Compass Part 2 – Using Your Compass and Map Together
In the first part of our discussion, “How to Use a Compass” we learned how to take a bearing. This is a great resource while out in the wilderness when your destination is visible. But what do you do if you can’t see your destination? A map to go with your compass is the answer. It takes a fair amount of skill to use these tools together and though we intend to teach you the basics in this post, we recommend taking a course in navigation to address your specific questions and provide practice in a safe environment.
Selecting a Compass
For use with a map, you’ll appreciate a compass that:
- Can be adjusted for magnetic declination
- Offers a long base-plate
- Has a built-in protractor
- And is scaled in two degree increments
It’s important to avoid metallic objects while using your compass. To get an idea just how much your compass will be affected, play with your compass around all kinds of metal objects like your belt buckle, certain jewelry, even your pocket knife. When you’re ready to take your bearing(s) avoid setting your map and compass on the hood of the truck or metal picnic table.
Adjusting Your Compass for Magnetic Declination
Compasses are invaluable in the wilderness because they’re designed to point out our path in reference to North. But understanding the difference between magnetic north and true north are important distinctions when using a compass and a map together. This difference is called magnetic declination and your compass will need to be adjustable to account for it. Read your specific compass owner’s manual and follow the instructions to adjust your compass. It’s good to understand that magnetic north is different than true north and is not a number you can memorize in comparison to true north because it changes depending on where you are and when you are—or rather it changes over time. It is important to be accurate when setting declination because 1 degree off can result in nearly 920 feet off course over 10 miles.
There are many online resources that help you to determine the exact variance. We like this site: www.ngdc.noaa.gov. Your map should tell what to set your compass to—what number of degrees you will need to adjust the compass to take accurate bearings where you’re navigating. Purchase an updated map to insure its declination value is accurate.
How to Take a Bearing on a Map
Now that you have adjusted your compass to account for the magnetic declination, you can take your bearing on the map. We won’t cover map reading in this post, but be aware that knowing how to read your map is crucial to this process and will make your trip much more pleasant since you’ll have a better idea what to expect from the terrain.
Lay your map out on a metal-free flat surface (even nail heads on picnic tables can throw your compass off). Find your starting point and your end point. Mark these on the map.
Next place your compass on the map and use one side of the baseplate to draw a line between your starting point and your destination (refer to the picture below for a review on the parts of a compass). Be sure the side of the compass you use has the direction of travel arrow pointing towards your destination.
With your compass still in place find true north by turning the dial until the two norths are lined up. Some experts refer to it as putting the needle in the shed or “red in the shed.” The direction of travel arrow will now be pointing towards your destination. Whatever the dial reads at the direction of travel arrow is your bearing (example 146 degrees).
Now you can put your map away (but keep it handy) and follow that bearing all the way to your destination.
Unknowns always arise in the field. We recommend practicing with your map and compass in a place you know well before you go out exploring with them. And as mentioned before, consider taking a class in navigation. We hope you enjoy this rewarding new skill and find your way outdoors soon!