Which North Pole does Santa Claus live at?

• True North– The earth’s axis of rotation

• Magnetic North– Where your compass points

• Grid North– Where the UTM grid lines “point” to.

True v.s. Magnetic North

• Depending on where you areThe angle between true and magnetic north will be different.

What is the difference here?

• Fruitvale Ave. is aligned with True North.

• So are the edges of parking lots 4 & 5.

• Let’s go take a bearing along the edge of lot 4 and see what we get…

• <parking lot declination diagram>

USA Declination Map

World Declination Map

Declination Diagrams

Declination changes over time

• Here in Northern California it changes by about 1° every 20 years.

• The declination shown on your topo map may be out of date.

• What about declination displayed by my GPS?– It probably correct as of the date of

manufacture.

Declination Calculatorat www.ngdc.noaa.gov

Local Anomalies

• May be as much as 90 degrees– 3-4 degrees is common

• North of Kingston, Ontario; 90° of anomalous declination.• Kingston Harbor, Ontario; 16.3° W to 15.5° E of anomalous

declination over two kilometers (1.2 miles); magnetite and ilmenite deposits.

• Savoff, Ontario (50.0 N, 85.0 W). Over 60° of anomalous declination.    

• Ramapo Mountains, northeastern New Jersey; iron ore; compass rendered useless in some areas.

• Near Grants, New Mexico north of the Gila Wilderness area; Malpais lava flows; compass rendered useless.  

Figuring out the adjustmentfrom magnetic to true

• My compass needle is pointing to the east of true north by 16°

Magnetic to True

• To adjust my compass to point to true north, I need to turn me bezel 16° to the west.

• That is the same as adding 16° to my magnetic bearing.

Declination

• East Declination

– Add declination to convert from Magnetic to True

– Subtract declination to convert from True to Magnetic

• West Declination

– Subtract declination to convert from Magnetic to True

– Add declination to convert from True to Magnetic

Two Schools of Thought• Set it and forget it

– Adjust for the declination in your compass. – All bearings will be true.– No conversion required to use it on a map.– Don’t forget to check the setting occasionally.– Don’t forget to change it when you go somewhere else.

• Set it to 0°, and always think about it– All bearings will be magnetic.– Conversion to true is necessary for map work.– Works with all compasses.– You are more likely to remember how declination

works.

No bearing is complete without the word True or Magnetic

following it.

• Don’t make people guess, say it!

Inclination or Dip

• The earth’s magnetic field is not always parallel to the surface.

• Thus compass needles need to be balanced• A compass needle balanced for the northern

hemisphere may rub the inside of the capsule in the southern hemisphere.

• Some compasses are designed for worldwide use.