North
Reference
At which North Pole does Santa Claus live?
True North
The earth’s axis of rotation
Magnetic North
Where your compass points
Grid North
Where the UTM grid lines “point” to
Grid Nerd
The North Reference
you choose
determines where 0° is
when you measure an angle
with your protractor or compass.
MN
MN
0° 25'
GN
0° 25'
15°
GN
5 320
295 300
305
0 285 290
0 245 250
255 260 26
5 270 275 28
30
30
35
40
9
8
7
6
5
4
3
2
65 70 75
80 85 90
95 100 105
11
0
80 E 1
0
0
12
2
5 10 15
60
60
240 260W280
0 355 0
20 25
1:24,000 U
T
M
G
ri
d
Each mark
is 100 mete
rs
55
40
20
325 330
335 340 34
5 35
50
20
0
N
310
31
45
340
320
15°
140
20
0
True v.s. Magnetic North
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…
USA Declination Map
World Declination Map
High Definition Geomagnetic Model
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out of date.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.
Magnetic Poles
North Pole
South Pole
2010
2000
2000
1600
1700
1800
1900
1900
1800
1700 1600
Declination Calculator
at 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. 33'
Using your GPS & compass
to measure
current local magnetic declination
d > 300m
MN
GN
14°
GPS
GOTO WPT001
Bearing 214° True
Compass
Bearing to Palm
200° Magnetic
Current Local Magnetic Declination is
14° East of True North
WPT001
Angular Error in
GPS Bearing to Waypoint
tan α
10m
x
-1
α
d
x
10m
α tan
d
α
100m
200m
300m
400m
500m
600m
700m
800m
900m
1000m
6°
3°
2°
1.4°
1.1°
1.0°
0.8°
0.7°
0.6°
0.57°
Using your map & compass
to measure
current local magnetic declination
Compass
Trail Jct -> Peak
52° Mag.
40
03
33
350 0
10 2
0
30
MN
40
50
03
10
0
32
70
260 270 280 290
30
60
14
0
23
30
01
24
12
50
02
80 90 100 110
From the map
Trail Jct -> Peak
68° True
Current local
magnetic declination
is (68 - 52) 16° E. of True North
1° 33'
GN
16°
0
15
60
01
170 180 190 200
02
20
21
Check you compass & sighting technique
using these methods and the declination for the area
• Find some place near your home to establish your
personal compass testing location.
• Identify several features, at least 1km away, that you
can sight on.
• Use a map to determine True bearings to these
features. Convert these bearings to Magnetic using
the calculated declination for the area.
• Check your compass and technique. Experiment with
the your gear to see if it influences your compass.
• Keep notes, so you can repeat this in the future.