A simple magnetic compass can help you keep a map oriented and follow a chosen direction when a phone or GPS is unavailable. It cannot tell you whether a road is open, whether a bridge is safe, where a shelter has space, or which route officials currently recommend. Start by learning the compass and practicing with a current map in a familiar, low-risk place. During an actual disruption, follow official instructions and current road information before using a compass to support a trip.
What a compass can and cannot show
A compass responds to Earth’s magnetic field. Its needle points toward magnetic north, which is different from geographic, or true, north. The difference between those two directions is called magnetic declination. Declination varies by location and changes with time, so a compass reading only becomes useful when you connect it to the map, area, and date you are using. The USGS explanation of declination gives the basic distinction.
The compass can help you keep a selected direction while you compare your surroundings with a map. It can also help you turn a map so its roads, rivers, property lines, and other symbols line up with what you see. That makes a paper map easier to read when a phone battery is low or a service connection is unavailable. A compass does not create a route. It does not know about a washed-out road, a closed gate, a flood, a fire perimeter, a damaged bridge, or an evacuation order.
Treat it as one part of a household travel plan. A current map, official alerts, road information, visible conditions, and communication with the people traveling with you remain separate needs. Using a paper map when your phone is unavailable explains why map date, scale, symbols, and current-route limits matter alongside the compass.
The parts of a basic baseplate compass
Many simple baseplate compasses share a small set of parts. The magnetic needle moves inside a housing, with one end marked for north. The direction-of-travel arrow points away from the compass and shows the direction you intend to follow. A rotating dial, often called a bezel, surrounds the housing and carries degree markings. Inside the dial, an orienting arrow and parallel orienting lines help you match the compass with north-south lines on a map.
The clear baseplate lets you place the compass over a map. Some models add a ruler, scales, a magnifier, or a declination adjustment. Markings and controls differ, so read the instructions for the actual model before relying on a feature. A compass that looks familiar may still use a different adjustment or reading method.
Before practice, hold the compass level enough for the needle to move freely. Keep it away from belt buckles, keys, a vehicle, a metal table, a phone case with magnets, and other iron or steel objects. The USGS method for using a compass describes how nearby metal can affect a reading.
Cardinal directions and bearings
The four cardinal directions are north, east, south, and west. A bearing gives a more precise direction as an angle measured clockwise from north. North is 0 or 360 degrees, east is 90 degrees, south is 180 degrees, and west is 270 degrees. Directions between them use the degrees in between.
For a household practice, imagine that you are checking a route from your home to a familiar library or community center. You are not treating that destination as an emergency shelter, and you are not assuming that the route will remain open. You are using a known place to learn what a bearing means. If the map shows the destination generally east of your starting point, the direction is near 90 degrees. A more exact line on the map could produce another bearing.
A bearing is a direction reference, not a promise that you can walk or drive straight to the destination. Roads curve, private property interrupts some paths, and terrain or weather can change what is practical. On a real trip, compare the bearing with roads and landmarks on the map, then follow the route that is actually open and appropriate. The USGS bearing method provides the degree relationships used here.
True north, magnetic north, and declination
Map north normally refers to true north, the direction toward the geographic North Pole. A magnetic compass points toward magnetic north instead. Magnetic declination is the angle between them at a particular place and time. It may be shown in the margin of a USGS map, but a printed value can become dated as the magnetic field changes.
Use the declination information for the map area and date rather than borrowing a number from a different town or an old map. If the value is unclear or the trip matters, confirm the current value through the USGS or NOAA resource appropriate to your map area. Do not make up an adjustment because the compass seems slightly off.
Some compasses have adjustable declination. A small setting changes the relationship between the compass’s orienting arrow and its magnetic needle, allowing the compass to account for the local value. Other compasses have no such adjustment. With a non-adjustable compass, the declination correction must be applied according to that compass’s instructions and the procedure used with the map. The USGS discussion of adjustable-declination compasses explains why the setting and the map value must match.
Do not copy an arithmetic example from one compass manual into another model. The direction of the correction depends on the local declination and the procedure. If you cannot identify the correct setting, use the model instructions and seek qualified map-and-compass instruction before depending on the reading for unfamiliar travel.
How to orient a map in a familiar place
Practice on a table or at a nearby open space where you already know the surroundings. Choose a map that covers the place and note its title, date, and declination information. Move away from vehicles, rail lines, metal fences, and other objects that can disturb the needle.
Place the compass on the map. Keep the straight edge or baseplate parallel to a north-south line on the map, with the direction-of-travel arrow pointing toward the top of the map. Turn the rotating dial so its orienting lines run in the same direction as the map’s north-south lines. Account for the local declination using the map and the compass instructions.
Then rotate the map and compass together until the magnetic needle sits over the orienting arrow in the position specified by your declination setting. The map and the compass now face the same general direction. Check the result against a landmark you recognize. Roads, a building, a ridge, or a waterway should appear in the expected relationship to your position. If they do not, stop and check the map orientation, declination, needle movement, and nearby metal before acting on the reading. The USGS map-orientation procedure shows this relationship step by step.
Map orientation does not verify the map’s information. A map may omit a new road, show a route that is now closed, or lack a hazard that has developed since publication. It also does not identify a safe crossing, an open building, or a place where authorities want people to go. Keep those questions with current official information.
Metal interference and other reading problems
Iron and steel can pull the needle away from the Earth’s magnetic field. A belt buckle close to the compass, a vehicle hood, a metal picnic table, railroad tracks, or another large metal object can change the reading. A phone or accessory may also contain magnets. If a reading seems inconsistent, move to a clear spot and take it again instead of trying to compensate by guessing.
Other problems are easier to prevent through practice. Holding the compass at an angle can keep the needle from moving as intended. Reading the wrong end of the needle, setting the bezel against the wrong line, or confusing true north with magnetic north can put the map and travel direction out of agreement. Keep the compass and map together while checking the sequence, and write down the map date and declination value you used.
A compass is not a current route plan
During an emergency, travel advice can change quickly. An official warning may direct residents to shelter, evacuate, avoid a road, or wait for further instructions. A compass cannot interpret that message. The alerts and message-backup Note can help you keep official updates available when a phone or power source is unreliable.
If an authority gives a route or destination, follow the direction and conditions attached to it. Check current road information before leaving, and keep checking when conditions can change. If landmarks, the map, weather, terrain, traffic, or official instructions disagree with your planned direction, stop and reassess. Do not press ahead because the bearing looks correct.
For household planning, tell a trusted person where you intend to go, who is traveling, and when you expect to check in. Stay with companions when possible, consistent with the National Park Service hiking safety tips. Account for the people, pets, mobility needs, medications, and communication needs that change the trip. A compass does not supply those decisions, and a familiar route is not automatically suitable during a disruption.
A simple practice check
Use a familiar low-risk route, such as a walk between two nearby public places, only when conditions are ordinary and the route is open. Bring the actual compass, the current map, the model instructions, and a pencil. Record the map name, date, declination information, and the place where you practiced.
First, identify the needle, direction-of-travel arrow, bezel, orienting arrow, orienting lines, and baseplate. Next, orient the map away from metal. Compare two visible landmarks with the map and describe their cardinal directions from your position. Set a bearing toward one landmark, then check the map and surroundings before taking any steps.
The point of practice is to notice disagreement early. If the needle does not settle, metal may be nearby. If the map and landmark do not match, check orientation and declination. If an official notice, weather change, closed route, or unsafe condition changes the plan, the plan changes. Record what happened so the next practice is more useful.
Frequently asked questions
Does a compass point to true north?
No. A magnetic compass responds to Earth’s magnetic field and points toward magnetic north. True north and magnetic north differ by the local magnetic declination, which varies by location and time.
What should I do if my map has no declination value?
Use a current declination value for the map area from an appropriate USGS or NOAA resource, and follow the instructions for the compass model. Do not transfer a value from a different area or assume an old value still applies.
Can I use a compass near a car?
A vehicle and other iron or steel objects can interfere with the needle. Move away from the vehicle and recheck the reading in a clear place before making a direction decision.
Is a compass enough for evacuation travel?
No. Pair it with current official instructions, current road information, a suitable map, visible conditions, communication, and practice appropriate to the trip. A compass cannot tell you whether a road, bridge, shelter, or crossing is currently safe or open.
Should I practice before putting a compass in a household kit?
Yes. Read the model instructions, orient a current map in a familiar place, and record the date and declination information used. Seek qualified instruction before depending on a compass for travel beyond your experience.
Your next check
Take the compass and map you would actually keep with household supplies. Read the compass instructions, locate the map’s declination information, and practice orienting the map away from metal. Record the map date and setting. The finished check is modest but useful: you can identify the basic parts, match the map and compass to the correct declination information, and recognize that a compass supports a plan without replacing current maps, official warnings, route checks, or appropriate training.