Magnetic Declination

“Declination: A Noun. The horizontal angle between the true geographic North Pole and the magnetic North Pole, as figured from a specific point on the Earth.” www.dictionary.com

 Declination is a term that causes “brain cramps” for many of my students in my map and compass classes. When I mention Magnetic Declination eyes roll.

The web site www.magnetic-declination.com has an excellent discussion of what declination is and what causes it:

“Magnetic declination varies both from place to place, and with the passage of time. As a traveler cruises the east coast of the United States, for example, the declination varies from 20 degrees west (in Maine) to zero (in Florida), to 10 degrees east (in Texas), ......the magnetic declination in a given area will change slowly over time, possibly as much as 2-25 degrees every hundred years or so.......... Complex fluid motion in the outer core of the Earth (the molten metallic region that lies from 2800 to 5000 km below the Earth's surface) causes the magnetic field to change slowly with time."

Land navigation is based on the relationship to the North Pole; also known as “true north.  The measure of degrees of direction in relation to true north is called “degrees true.”  Maps are laid out in degrees true.  Land features (buttes, mountains, streams) on a topographic map are in reference to degrees true.  By that I mean the bearing from one mountain peak to another will be referenced in degrees true.  The map below illustrates that point. 

Magnetic compasses do not point to true north (the North Pole); the magnetic needle points to an area that could be considered the magnetic North Pole. 

As illustrated below, declination data can be found in the diagram at the bottom of a USGS topographic map, (on some commercially produced maps it can be hard to find.) 

Because declination changes over time, I recommend that map declination information be verified at www.magnetic-declination.com.   This is essential in the Pacific Northwest where maps are notoriously out of date in terms of road,  and city data.

So, how do we make this simple?  How do we convert magnetic to degrees true?

I could do the math.  In Oregon, where I live, the magnetic declination is 15.6° East declination.

My recommendation: have the compass do the work so that there is no confusion with the math.

To do this, I need to choose a compass that can be adjusted for declination.  Some examples are the Silva Ranger or the Suunto M3.

With one of these compasses, the compass dial or housing is adjusted and rotated manually.  Both the Suunto and Silva Ranger come with a small, flat adjusting tool.  Consult with owner’s manual that came with the compass.

If declination is Easterly (Western U.S.) I will rotate the dial causing the baseplate’s orienting arrow to move in a clockwise direction.

   If declination is Westerly (Eastern U.S.) I will rotate the dial causing the baseplate’s orienting arrow to move in a counter-clockwise direction.

Now, adjust the dial and align the red magnetic needle on top of the orienting arrow (the red arrow engraved on the baseplate) the compass will provide directions in degrees true.

Accurate Compass Readings

I found these recommendations a while back when I was researching techniques for using a magnetic compass.  A small error when using a compass can result in significant error in measurement on the ground.

To obtain accurate readings when using a compass:

• Ensure the compass has been adjusted for declination. 
• Hold the compass level and steady so the needle swings freely.
• Hold the compass about waist high in front of the body, except when using a compass with a sighting mirror or a sighting type compass.
• Raise and lower eyes when taking a bearing, do not move your head. Always use the same eye when taking bearings.
• Directly face the object that is being measured.
• Magnetic fields will give incorrect compass readings. Avoid taking readings near magnetic fields such as steel, iron (ferrous metals), vehicles, rebar, and clipboards. Even belt buckles, glasses, and rings can interfere with the compass reading.
• Take bearings twice. 
• Adjust for magnetic declination as appropriate.
• Follow the direction of travel arrow, not the compass needle, when walking a bearing. Always follow the line indicated by the compass rather than relying on judgment as to the direction.
• Use back bearings to ensure you are on track when navigating.
  

  
• Compare compass reading with those of your GPS.
• Remember that a GPS receiver's compass must be calibrated after every battery change.

Getting Accurate Compass Readings

I found these recommendations a while back when I was researching techniques for using a magnetic compass.  A small error when using a compass can result in a significant error in measurement on the ground.

To obtain accurate readings when using a compass:

• Ensure the compass has been adjusted for declination. 
• Hold the compass level and steady so the needle swings freely.
• Hold the compass about waist high in front of the body, except when using a compass with a sighting mirror or a sighting type compass.
• Raise and lower eyes when taking a bearing, do not move your head. Always use the same eye when taking bearings.
• Directly face the object that is being measured.
• Magnetic fields will give incorrect compass readings. Avoid taking readings near magnetic fields such as steel, iron (ferrous metals), vehicles, rebar, and clipboards. Even belt buckles, glasses, and rings can interfere with the compass reading.
• Take bearings twice. 
• Adjust for magnetic declination as appropriate.
• Follow the direction of travel arrow, not the compass needle, when walking a bearing. Always follow the line indicated by the compass rather than relying on judgment as to the direction.
• Use back bearings to ensure you are on track when navigating.
  

  
• 
  

Taking Good Care of a Compass

A few thoughts on taking care of your compass and what to look for before you go hiking in the backcountry.

Remember that the correct operation of the compass is dependent on the action of the magnetic needle to guide the hunter through the backcountry.  Lots of items in a pack and clothing can effect the needle.  Most understand that ferrous objects such as a rifle barrel, belt buckle, and car keys will deflect the magnetic needle.  Still, take a good look at what is in a day pack.  The batteries from the GPS receiver and a flash light may cause a compass needle to move.

High tension power lines and a vehicle’s electrical system may also cause a magnetic needle to deflect.  Moving a few steps from the vehicle should be sufficient.  One may have to move over one hundred feet from the power lines to avoid deflection.  (GPS Made Easy, Michael Ferguson.)

Some locations will have a high concentration of iron near the surface.  This is known as “local attraction.”  Such concentrations will cause the needle to move too.  Unlike declination, moving away from the immediate area may cause the deflection to stop.  The local Bureau of Land Management or Forest Service Office should be able to identify areas affected by local attraction.

 I recommend that a compass be stored away from electronics (e.g., GPS, radios), batteries and many metallic (knives, saw) objects found in a pack.  I don’t recommend going overboard on this but a compass could simply go in an exterior compartment, a shirt or coat pocket.  Attaching a brake away lanyard to a compass so that is worn around the next is a viable option. This would apply during the off season too; a little separation is a good thing.

It is possible for the magnetic needle to lose its polarity.  This is a function of time and manufacture.  With research, one can learn how to restore the magnetism.  That said, with the modern liquid filled compass this is probably more trouble than it is worth.  Occasionally, check the alignment of the compass.  In the small town where I live, residential streets are aligned true north and south.  Standing on the curb on such a street provides a quick verification of how the compass is working.  To me verification means that the compass direction will mirror that of the street; if the street tracks true north then the adjusted compass should provide a bearing to true north.

At the end of the hiking or hunting season take a look at the compass.  Flush away dirt or sand that may be on the baseplate or sighting mirror.  Look for bubbles that may appear internally and adjacent to the compass needle.  A small bubble may not be something to worry about but a large bubble may impact how the needle swings and moves.  A compass with a large bubble should be permanently removed from the hiker’s kit.

Lastly, keep in mind that a quality compass will retail for $20 or more.  Also, a quality compass can be mechanically adjusted for declination.  Such a compass is a precision piece of equipment.  This is especially true of the Silva Ranger style or the Brunton Eclipse models.  Note that I am prejudice (won’t buy them) towards the cheap stuff found on the racks of the major box sporting goods stores.  If a hunter is willing to spend hundreds of dollars on a rifle scope why not spend a bit more for a decent compass; it can make a huge difference. 

That Old Compass

Grandfather’s compass from decades ago may no longer be the best selection for the hiker.  The image below is of a compass made between 1910-1920.  Though the dial is fairly detailed, the accuracy may be reduced due to the polarity of the magnetic needle. 

 In general terms, the polarity is how the magnetic needle will react to the earth’s magnetic field.  Over a period of almost 100 years, the compass’ magnetic needle may not move in relation to magnetic north as it did when new; that could mean the differences of several degrees.  

To prove this point take a new baseplate compass and compare the two (do not hold them near each other.)  A navigator can also compare it a new compass or a location where a street or trail is known to run true north.

My recommendation then is to leave the old antique compass in a place of honor at home.  It is time to consider buying a new compass.

Magnetic Compass Accuracy

Navigating with a magnetic compass is a skill that takes study and practice.

When plotting the hiker’s position on a map the objective is to have three lines of bearing intersect just like in the image below; this is a position fix.  That is “pin point” accuracy. This is hard to do with a magnetic compass and may not be achievable.

Blake Miller/Outdoor Quest Image

Many factors impact accuracy.  Some the hiker will have no control over.  

These include:

1. Visual acuity (e.g., how well the hiker can see.)
2. Polarity of the compass’ magnetic needle – does it point in the right direction? Polarity may change over time such that the magnetic needle may no longer work accurately.
3. Smooth movement of the magnetic needle.
4. Alignment of the compass dial to the compass housing.
5. Local attraction – Similar to declination, local attraction is magnetic interference unique to a specific location.  It may be caused by buried metal objects or an unusually high concentration of iron or nickel in the ground.
6. Lack of distant objects to sight on.
7. Weather (e.g., Fog, clouds, and smoke.)
8. Terrain may hide the objects that the hiker wants to sight with the compass.

The hiker does have control over the following.

1. Purchasing a quality compass such as the Silva Ranger.
2. Correctly adjusting for declination.
3. Staying away from iron and steel objects such as a car, high tension power lines and a hunting rifle.
4. Practiced sighting techniques.
5. Practiced with the procedures of plotting the various lines of bearing.

Blake Miller/Outdoor Quest Image

 The image above closely represents what the hiker will have to deal with and accept.  The crossed lines of bearing provide a rough approximation of a position plotted on the map.

Terrain Association will further "dial in" the hiker's backcountry position.

Blake Miller/Outdoor Quest Image

The image above represents the error of the plotted lines of bearing.  Notice that the lines of bearing have poor angular separation. But by using terrain association the hiker might be able to refine the position fix.  If the hiker is near the river and on the on the river's east side then the position close the road  will better define location.

Navigation is not hard but it does take practice; it is a perishable skill.

When in the wilderness compare both map and compass with a GPS when possible.  Hiking companions should compare their work too.

Read other compass related posts:

     Buying a Magnetic Compass

     Declination

A solid reference is June Fleming's Staying Found and Bjorn Hjellstrom's Be Expert With Map and Compass.

Nine Navigation Steps to Take at the Trail Head.

The following are nine quick navigation steps to take to ensure one’s navigation kit is set up to best support a hike.

Blake Miller/outdoor quest image

1.     GPS Batteries – load fresh batteries and carry extra for both the GPS and flashlight.

2.     Calibrate the GPS receiver’s compass after every battery change.

3.     Magnetic Compass adjusted for declination – Visit www.magnetic-declination.com for the most current declination value.  Declination changes over time (how old is that map?) and location.

4.     Dump the junk – How many waypoints are stored in the waypoint manager file.  Dump the old waypoints to the absolute minimum; this helps to keep navigation simple.

5.     Match the GPS receiver’s compass to the magnetic compass and the map.   .  Maps are usually set to degrees true.  Have the GPS and Magnetic compass match the topo map.

6.     Erase old track data – clean up the old the track (bread crumb trail) information.  Get rid of 

Blake Miller/outdoor quest image

the clutter.

7.     Remember to stow the maps.  I use maps from www.caltopo.com and will occasionally carry maps from a hiking guides.  Maps are stowed in a zip lock gallon bag or rugged water proof map case.

8.     Mark a waypoint – Give key waypoints a name like “trl hed” or “camp.”  Select waypoint manager to verify that the information has been saved to memory.  If “trl hed” can be viewed on the waypoint manager file or viewed from the map page the hiker is all set.

9.     

Blake Miller/outdoor quest image

Orient the map at the trail head.

Everyone in the hiking group should be on the same page in regard to navigation settings.

Finding North

 I randomly pulled a book from my outdoor library and found a section on back country travel and survival.   My book was printed in the late 1950's.  To say Tt was dated is obvious.

I skimmed through the navigation section and began to read about determining True North (000 degrees).

The chapterI soon began a discussion of using the north star to find True North.  Nice idea but finding True North is a challenge.  The north star doesn't stand out as some material would have your think.  Weather can have a huge impact on locating that star.

My reference talks about determining declination by comparing magnetic north with the bearing of the north pole.

Interesting idea but it's a bit tedious.

Let's keep this simple.

First, lets start with a quality adjustable magnetic compass.  I'd suggest that the hiker consider the Silva Ranger 5/15 or one similar by Brunton or Suunto.  These are frequently found at REI, Cabala's and Sportsman's Warehouse.

Second, determine the coordinates of the area that that one will travel through.

Third, visit www.magnetic-decllination .com.  The hiker will find lot of options but the key thing one is looking for is the declination of the area to be traveled through. One can enter Latitude an Longitude of the area or a noun name like Bend, Oregon.

Read the compass manufacturer's instruction  and adjust the compass as directed to find north.

Take a look at my post about buying a compass    .Buying a Compass

Using Your Cell Phone In The Backcountry

Last month Jenny Rough wrote an interesting article about why it is a mistake to count  on a cell phone when you go hiking.  Her article was featured in the Washington Post.

She stressed that basic navigation "is a use-it-or-lose-skill.  How true.

The thrust of the post is that hikers have an over dependence of electronic navigation while forsaking the rudimentary  principles of using a map and compass. 

Take a look at Jenny's post.

Visit my other articles on land navigation too:

• Compass Tips
• GPS Tune-up
• Terrain Association

• A Hiker's Trip Plan

What Is An Azimuth

An azimuth is the angular direction to an object.  Azimuths are described commonly in degree increments from either true, magnetic or grid north.

In the world of recreational navigation, GPS receiver operations and orienteering the use of the term “bearing” has become synonymous with azimuth.

Azimuth direction is measured from north clockwise in 360° increments. The point from which the azimuth originates is from the center of an imaginary circle.  This imaginary point is the operator.

Azimuth can be measured with a magnetic compass, a map and by rough estimation using the sun and North Star.

Azimuths can be expressed in degrees true and degrees magnetic.  Degrees true uses the north pole as the principle reference while degrees magnetic refers to reference from the magnetic pole.

Outdoor Quest Image

For more information on bearings and azimuth read Making Sense of The Declination Diagram.

Magnetic Declination

“Declination: A Noun. The horizontal angle between the true geographic North Pole and the magnetic North Pole, as figured from a specific point on the Earth.” www.dictionary.com

 Declination is a term that causes “brain cramps” for many of my students in my map and compass classes. When I mention Magnetic Declination eyes roll.

The web site www.magnetic-declination.com has an excellent discussion of what declination is and what causes it:

“Magnetic declination varies both from place to place, and with the passage of time. As a traveler cruises the east coast of the United States, for example, the declination varies from 20 degrees west (in Maine) to zero (in Florida), to 10 degrees east (in Texas), ......the magnetic declination in a given area will change slowly over time, possibly as much as 2-25 degrees every hundred years or so.......... Complex fluid motion in the outer core of the Earth (the molten metallic region that lies from 2800 to 5000 km below the Earth's surface) causes the magnetic field to change slowly with time."

Land navigation is based on the relationship to the North Pole; also known as “true north.  The measure of degrees of direction in relation to true north is called “degrees true.”  Maps are laid out in degrees true.  Land features (buttes, mountains, streams) on a topographic map are in reference to degrees true.  By that I mean the bearing from one mountain peak to another will be referenced in degrees true.  The map below illustrates that point. 

Magnetic compasses do not point to true north (the North Pole); the magnetic needle points to an area that could be considered the magnetic North Pole. 

As illustrated below, declination data can be found in the diagram at the bottom of a USGS topographic map, (on some commercially produced maps it can be hard to find.) 

Because declination changes over time, I recommend that map declination information be verified at www.magnetic-declination.com.   This is essential in the Pacific Northwest where maps are notoriously out of date in terms of road,  and city data.

So, how do we make this simple?  How do we convert magnetic to degrees true?

I could do the math.  In Oregon, where I live, the magnetic declination is 15.6° East declination.

My recommendation: have the compass do the work so that there is no confusion with the math.

To do this, I need to choose a compass that can be adjusted for declination.  Examples are the Silva Ranger or the Suunto M3.

With one of these compasses, the compass dial or housing is adjusted and rotated manually.  Both the Suunto and Silva Ranger come with a small, flat adjusting tool.  Consult with owner’s manual that came with the compass.

If declination is Easterly (Western U.S.) I will rotate the dial causing the baseplate’s orienting arrow to move in a clockwise direction.

   If declination is Westerly (Eastern U.S.) I will rotate the dial causing the baseplate’s orienting arrow to move in a counter-clockwise direction.

Now, adjust the dial and align the red magnetic needle on top of the orienting arrow (the red arrow engraved on the baseplate) the compass will provide directions in degrees true.

Getting Accurate Compass Readings

I found these recommendations a while back when I was researching techniques for using a magnetic compass.  A small error when using a compass can result in a significant error in measurement on the ground.

To obtain accurate readings when using a compass:

• Ensure the compass has been adjusted for declination. 
• Hold the compass level and steady so the needle swings freely.
• Hold the compass about waist high in front of the body, except when using a compass with a sighting mirror or a sighting type compass.
• Raise and lower eyes when taking a bearing, do not move your head. Always use the same eye when taking bearings.
• Directly face object that is being measured.
• Magnetic fields will give incorrect compass readings. Avoid taking readings near magnetic fields such as steel, iron (ferrous metals), vehicles, rebar, and clipboards. Even belt buckles, glasses, and rings can interfere with the compass reading.
• Take bearing twice. 
• Adjust for magnetic declination as appropriate.
• Follow the direction of travel arrow, not the compass needle, when walking a bearing. Always follow the line indicated by the compass rather than relying on judgment as to the direction.
• Use back bearings to ensure you are on track when navigating.