USGS Education

These directions assume your orienting arrow lines up with the North indicator on your compass dial, meaning the compass has **NOT** been adjusted for declination.

A) Obtain the local magnetic declination for the area represented on your map. At the bottom of every USGS map is a diagram that displays the difference & direction between **true** **north** (represented as a star), **grid north** (abbreviated as "GN"), and **magnetic north** (abbreviated as "MN"). **Magnetic declination **is the number of degrees and direction between **true north** and **magnetic north.** Because declination varies over time, it is advisable to get a reasonably current figure. If your USGS map is more than 15 years old (the declination date appears in the diagram), here’s an easy-to-use website that gives you only the information you need for your specific area:

**Magnetic Declination Calculator**

If magnetic north is **east** of true north, the local declination is **positive**.

If magnetic north is **west** of true north, the local declination is **negative**.

B) Draw a line on the map that connects your starting point with the destination (your "map bearing"). Extend the line all the way through the map border (the "neat line").

C) Distance yourself from any nearby metal such as keys, belt buckle, desk, car, fence, etc. Place the compass on the map so the needle’s pivot point is ** directly** over the intersection of your map bearing and neat line.

D) Rotate the dial until compass ring north agrees with map north. Read your map bearing from the compass dial. Make sure the bearing agrees with your direction of travel – for example, if you intend to travel due east, the bearing is 90 degrees, not 270 degrees.

E) __Do this step mentally – don’t turn the compass dial__: If the local declination is **positive**, then **subtract **the declination amount from the bearing you just derived. If the local declination is **negative, **then **add **the declination amount to the bearing you just derived.

F) Turn the compass dial until the figure you calculated in step E lines up with the index line.

G) Lift the compass off the map, and with the direction of travel arrow pointing directly away from you, rotate your body and the compass all in one motion until the red magnetic needle overlays the orienting arrow.

H) Sight a landmark along this bearing, and proceed to it. Repeat this step until you reach your destination.

These instructions describe how to navigate from a known location on a topographic map to another known location on the same map. These directions assume your orienting arrow lines up with the North indicator on your compass dial, meaning the compass has **NOT** been adjusted for declination.

A) Obtain the local magnetic declination for the area represented on your map. At the bottom of every USGS map is a diagram that displays the difference & direction between **true** **north** (represented as a star), **grid north** (abbreviated as GN), and **magnetic north** (abbreviated as MN). **Magnetic declination** is the number of degrees and direction between **true north** and **magnetic north.** Because declination varies over time, it is advisable to get a reasonably current figure. If your USGS map is more than 15 years old (the declination date appears in the diagram), here's an easy-to-use website that gives you the information you need:

**Magnetic Declination Calculator**

If magnetic north is **east** of true north, the local declination is **positive**

If magnetic north is **west** of true north, the local declination is **negative.**

B) Draw a line on the map that connects your starting point with the destination (your "map bearing").

C) Distance yourself from any nearby metal such as keys, belt buckle, desk, car, fence etc.

D) Place the compass on the map so the baseplate is parallel to the line you drew. Make sure the direction of travel arrow points to your destination.

E) Rotate the dial until compass ring north agrees with map north. Do **not** move the compass when you rotate the dial.

F) Remove the compass from the map and, with the direction of travel arrow pointing directly away from you, rotate your body and the compass all in one motion until the red magnetic needle overlays the orienting arrow.

G) If local declination is **positive**, then **subtract** the declination amount (turn the dial **clockwise**). If local declination is **negative, **then **add **the declination amount (turn the dial **counter clockwise**).

H) Again, with the direction of travel arrow pointing directly away from you, rotate your body and compass all in one motion until the red magnetic needle overlays the orienting arrow. Sight a landmark along this direction of travel and proceed to it. Repeat this step until you reach your destination.

A compass with adjustable declination allows you to rotate the orienting arrow independently of the compass dial. If you have such a compass, you may calculate your map bearing without adding or subtracting the amount of local magnetic declination. To calibrate your compass in this fashion, rotate the inner liquid capsule (or turn the screw with the key) until the orienting arrow deviates from the compass ring’s north indicator by the amount & direction of the local magnetic declination. For example, if local declination is 10 degrees east of true north, rotate the inner liquid capsule (or turn the screw with the key) until the orienting arrow points to 10 degrees east. If using M**ethod #1**, you do not need to add or subtract as indicated in step E; just make sure compass ring north (not the orienting arrow) agrees with map north as directed in step D. If using **Method #2**, skip steps G and H; again, be sure compass ring north (not the orienting arrow) agrees with map north as directed in step E.

Place the compass on the map so the baseplate parallels the north-to-south map *neat line* (the map border). Rotate the dial until compass ring North agrees with map North. Add or subtract the amount needed to adjust for local magnetic declination (subtract if local declination is positive, add if local declination is negative); if your adjustable declination compass is already calibrated for local declination, you don’t need to add or subtract, just make sure __compass ring North__ (not the orienting arrow) agrees with map North. Holding the map and compass steadily (the baseplate should still be on the north-to-south map *neat line*), rotate the map and compass all in one motion until the red magnetic needle overlays the orienting arrow. Again, make sure there is no interference from metal when you perform this (ex: rebar in concrete). Your map and your compass are now oriented to true north. Compare the physical features around you with your map to help derive your location on the map.

Let’s assume the local declination is 10 degrees east of true north, and the waypoint you wish to navigate to is directly north of your current location.

If using a compass **without** adjustable declination, set your GPS to **magnetic north. **Your GPS will indicate a bearing of 350 degrees must be followed to reach the waypoint. Dial 350 degrees on your compass. With the direction-of-travel arrow pointed __directly__ away from you, turn your body & compass in one motion until the red magnetic needle overlays the orienting arrow. Site a landmark along that bearing, and proceed. You will be traveling directly north toward the waypoint.

If using a compass **with** adjustable declination, set your GPS to **true north.** Your GPS will indicate a bearing of zero degrees must be followed to reach the waypoint. Adjust the declination on your compass so the orienting arrow points to 10 degrees east. Dial zero degrees on your compass. With the direction-of-travel arrow pointed __directly__ away from you, turn your body & compass in one motion until the red magnetic needle overlays the orienting arrow. Site a landmark along that bearing, and proceed. You will be traveling directly north toward the waypoint.

**Percent of slope **is determined by dividing the amount of elevation change by the amount of horizontal distance covered (sometimes referred to as "the rise divided by the run"), and then multiplying the result by 100. The "run" assumes you're traveling on an idealized flat surface – it does **not** account for the actual distance traveled once elevation change is factored in.

Example: let’s assume your climb gains **1,000** feet in altitude (the rise) and the horizontal distance as measured on the map is **2,000** feet (the run).

Multiply

Example: let’s assume your climb gains **500** feet in altitude (the rise) and the horizontal distance as measured on the map is **3,000** feet (the run).

Multiply

Example: let’s assume your climb gains **700** feet in altitude (the rise) and the horizontal distance as measured on the map is **500** feet (the run).

Multiply

**Angle of slope** represents the angle that’s formed between the run (remember it’s an idealized flat surface that ignores elevation change) and your climb’s angular deviation from that idealized flat surface. To calculate this, you divide the rise divided by the run, and then obtain the inverse tangent of the result.

Example: let’s assume your climb gains **1,000** feet in altitude (the rise) and the horizontal distance as measured on the map is **2,000** feet (the run).

Press the

Press the

Your angle of slope is

Example: Let’s assume your climb gains **1,000** feet in altitude (the rise) and the horizontal distance as measured on the map is **1,000** feet (the run).

Press the

Press the

Your angle of slope is

In this case, you know the "aspect," but you don't know the number of degrees.

using a compass **without** adjustable declination, make sure the direction of travel of arrow is pointing directly away from you. Now rotate the compass dial until the red magnetic needle overlays the orienting arrow. Observe the reading at the index line. If local magnetic declination is **positive,** then ** add **the necessary amount. If the local declination is

If using a compass **with** adjustable declination, make sure the direction of travel arrow is pointing directly away from you. If you haven’t done so already, adjust the declination so the orienting arrow deviates from the compass ring’s north indicator by the amount & direction of local magnetic declination. Turn the compass dial until the red magnetic needle overlays the orienting arrow. The number at the index line is the true direction you are facing.

In this case, you know the number of degrees, but don’t know what "aspect" to face (what direction should I face?).

Let’s assume you wish to face true north (zero degrees).

__Compass without adjustable declination__: turn the compass dial until zero is at the index line. If local declination is

__Compass with adjustable declination:__ turn the compass dial to zero. If you haven’t done so already, adjust the declination so the orienting arrow deviates from the compass ring’s north indicator by the amount & direction of local magnetic declination With the direction of travel arrow point directly away from you, rotate your body and compass together in one motion until the red magnetic needle overlays the orienting arrow. You are now facing true north.

Let’s assume the local magnetic declination is 10 degrees east of true north (a positive declination). Therefore, the needle always points to 10 degrees. Let’s also assume that although you don’t know what direction you’re facing, it coincidentally happens to be true north. If you rotate the dial until the red magnetic needle overlays the orienting arrow (implying, "What direction ** am** I facing?"), the reading at the index line will be 350 degrees; you must

If you're in an area where magnetic declination is __positive__, here's an easy way to remember:

WHAT DIRECTION ** AM **I FACING?

WHAT DIRECTION

The magnetic needle in a compass is attracted by the magnetism of the Earth, and therefore always points to the constantly shifting Magnetic North Pole. The Geographic North Pole is static and is located about 1200 miles north of the Magnetic Pole. Maps and directions are usually oriented toward the Geographic Pole, also referred to as "True North."

Magnetic declination is the direction and amount of variation between the Magnetic Pole and True North. The amount and direction of declination depends upon how those two poles align relative to a given point on Earth. When the two poles align, declination is zero, and the line of zero declination is termed the agonic line. At points west of the agonic line, a magnetic needle will point east of true north (positive declination). At points east of the agonic line, a magnetic needle will point west of true north (negative declination). There is a pattern, but it does not follow meridians or parallels. Isogonic lines are like magnetic contour lines – they trace a path of constant magnetic declination.