Compass and Map Use

This guide will help with the following 2 area

  1. How to use a Compass (including setting Declination)
  2. How to read a Topo-Map

How to Use a Compass

Knowledge of proper compass and map use can get you where you want/ned to go, and can also get you out of some dangerous situations.

Parts of a Compass

There are a multitude of compasses available.  Many of them share them share the features depicted below.

  • Direction of Travel
  • Declination Adjust
  • Rotating Bezel
  • Orientating Arrow
  • Orientating Lines
  • Rulers and Scales
  • Needle Housing
  • Magnetic Needle

Magnetic Declination and its Adjustment

Magnetic Declination is the variation between True North and magnetic North.  It varies by location and time.

Most topographic maps list declination in the legend.

Please note, however that declination changes over time. It's bets practice to check your map’s revision date. To get the most accurate reading, goto the National Oceanic and Atmospheric Administration (NOAA) website/

Orientating a Map

Being able to connect what is on your map versus what you see around you is a critical skill. The first step of this skill is orientating your map properly.

Keep in mind that Magnetic Declination must be accounted for before orientating your compass to you map.
  1. Slide your compass to have its side align with the vertical guide lines at the side of your map.
  2. Ensure your compasses Direction of Travel Arrow is pointing to the top of the map
  3. Rotate your compass bezel so that the Orientating Arrow is pointing up, aligned with the Direction of Travel Arrow on your compasses baseplate.
  4. While holding the map and compass steady, rotate yourself until the end of the magnetic needle is within the outline of the Orientating Arrow.

Now you have the map oriented correctly and can identify nearby landmarks on it. Take time to become familiar with your map and surroundings before you head off. And keep reading your map along the way: Staying found is far easier than finding yourself after you’re lost.

Using a Compass to Find a Bearing

We have set up our Compass to account for Magnetic Declination, and we have orientated our compass to the map, and our map to our surroundings.  Now it is time to create a bearing to move in a specific direction from a know point to a destination.

A Bearing is a precise way to describe a direction. For example, instead of heading “southwest” to arrive at a destination, you would follow a bearing of 210 degrees.

The four cardinal points on a compass, which split the circumference of the compass into four equal parts, are (going clockwise) North, East, South and West. Since there are 360º in the circumference, the cardinal points are separated by 360º/4 or 90º.

Bearings are always relative to a specific location on a map. 2 people in 2 different locations, following the same bearing, will travel parallel to each other and not arrive at the same place

Finding a Bearing Without a Map

Select a landmark. Rotate the bezel so that the Magnetic Needle aligns with the Orientating Arrow. Your bearing is the number that aligns with the direction you are pointing the compass.

Travel in a Direction With a Known Bearing

If you dont have a map but have been given a bearing on which to travel, turn the bezel so that the bearing aligns with the Direction of Travel Arrow. 

Get yourself orientated with the compass out in front of you and the Direction Travel Arrow pointing forward. Rotate to a direction that causes the Magnetized Needle and Orientating Arrow to align (called "Red in the Shed") to align.  This will force you to rotate to the correct bearing. Start your travel, keeping the Direction of Travel Arrow pointing forward, and the the Magnetized Needle and Orientating Arrow aligned with each other.

Plotting a Bearing Course on a Map

Here is a simple technique for plotting a bearing course on a map

1. Align the straight side edge of your compass on an imaginary line that connects your current location with your destination.  Ensure the the Direction of Travel Arrow is facing in the direction you want to travel.

2. Rotate your compass bezel so that the Orientating Arrow is aligned with north on the map.  Many compasses have guidelines to make this an easy task.

3. Observe your bearing on your compass.  This is the direction that you should travel from your current spot to the plotted destination.

4. Get yourself orientated with the compass out in front of you and the Direction Travel Arrow pointing forward. Rotate to a direction that causes the Magnetized Needle and Orientating Arrow to align (called "Red in the Shed") to align.  This will force you to rotate to the correct bearing. Start your travel, keeping the Direction of Travel Arrow pointing forward, and the the Magnetized Needle and Orientating Arrow aligned with each other.

Finding Your Position on a Map (Triangulation)

If your location is unknown, you can use triangulation to locate your position.

Locate 3 landmark/features in the observable landscape that you can correlate on a map.  It is best if these are not close to each other on the horizon. These would be things like mountain tops, river bends, rock outcroppings, etc.

Select the first landmark/feature, and point your compass towards it. Rotate the bezel so that the Magnetic Needle aligns with the Orientating Arrow. Next, place your compass on the map, with a corner of the compass touching the landmark. Rotate the compass to a direction that causes the Magnetized Needle and Orientating Arrow to align. Use the straight edge of the compass to draw a line.

Repeat the same process for landmark/features #2 and #3.  YOu current location is the intersection of these 3 lines.

How to Read a Topo Map 

A magnetized compass and a paper map are part of the Ten Essentials. Learning to read that paper topo map (short for topographic map) is every bit as essential. 

This article covers these concepts:

  • How contour lines help you visualize your terrain
  • How map scales work
  • Latitude and Longitude
  • Map Legends, symbols and other details
  • Where to find topo maps

Also read our companion article, How to Use a Compass. Then take a class with the REI Outdoor School or another outdoor organization and practice these skills until you master them.

Contour Lines

Contour lines indicate the steepness of terrain. Contour lines connect points that share the same elevation: Where they’re close together (they never intersect), elevation is changing rapidly in short distance and the terrain is steep. Where contour lines are wide apart, elevation is changing slowly, indicating a gentle slope.

topographic contour lines translated to steep slopes and gentle slopes

(REI.com)

Contour lines also indicate the shape of the terrain. Roughly concentric circles are probably showing you a peak, and areas between peaks are passes. Studying a topo map of a familiar area is a great way to learn how to match terrain features with the contour lines on a map.

2 D topographic contours translated as 3 D

(REI.com)

Index contour lines: Every fifth contour line is a thicker, “index” line. At some point along that line, its exact elevation is listed.

Contour interval: The change in elevation from one contour line to the next is always the same within the same map. Many maps have either a 40- or 80-foot contour interval: An 80-foot interval simply means that each contour line is 80 vertical feet away from the next closest line. You find the contour interval for your map in its legend.

Topographic example of contour intervals

(REI.com)

Every once in a while, a circle indicates a depression rather than a peak. A circle with tick marks inside it indicates a depression, rather than a peak. You should also see elevations decreasing as you get near the depression

Map Scales

Scale refers to the relationship between distance on a map and the corresponding distance on the ground. The scale represents this ratio in a fraction format. For instance, a 1:24,000 scale means 1 unit of measure on the map is equal to 24,000 of the same units of measure on the ground. Therefore, a 1:24,000 scale means that one inch on the map is equal to 24,000 inches (2,000 feet, 0.38 miles or 609.6 meters). The map scale is usually defined on the margin of the map

There are many different map scales. The United States Geological Survey (USGS) produces the most widely distributed topographic maps in the U.S. These are the 7.5-minute 1:24,000 scale, where 1 inch represents 2,000 feet. A scale of 1:25,000 is the standard for countries that use metric units, where 1 centimeter = 0.25 kilometers. 

The 7.5-minute quads are printed at a 1:24,000 scale, meaning that one unit on the map (e.g. one inch) equals 24,000 units in real life. For context, there are 63,360 inches in one mile (5280 feet per mile, 12 inches per mile) so one inch on the 7.5-minute maps equals 0.3788 miles. The standard contour interval is 40 feet.

How to choose the right scale for a hiking map

Medium-scale maps (e.g., 1:24,000) cover smaller areas in greater detail, whereas smaller-scale maps (e.g., 1:250,000) cover larger areas in less detail. The most important consideration in choosing a map is picking the correct scale. Ensure the scale will provide the level of detail required for its intended use. A few examples:

  • 1:250,000 scale: 1 inch ~ 4 miles (less detailed; adequate for driving to the trailhead)
  • 1:100,000 scale: 1 inch ~ 1.6 miles (detailed; sufficient for planning a hike)
  • 1:24,000 scale: 1 inch ~ 2,000 feet (more detailed; adequate for hiking the trail)

Latitude and Longitude Grid/Markings

Picture

Lines of latitude measure north-south position between the poles. The equator is defined as 0 degrees, the North Pole is 90 degrees north, and the South Pole is 90 degrees south. Lines of latitude are all parallel to each other, thus they are often referred to as parallels.

One degree of latitude is
60 nautical miles, 69 statute miles or 111 km.

One minute of latitude is
1 nautical mile, 1.15 statute miles, or 1.85 km.

Lines of longitude, or meridians, run between the North and South Poles. They measure east-west position. The prime meridian is assigned the value of 0 degrees, and runs through Greenwich, England. Meridians to the west of the prime meridian are measured in degrees west and likewise those to the east of the prime meridian are measured to by their number of degrees east.

Latitude and longitude can be noted as a decimal, or in degree - minute - second format.

Facts about lines of latitude. parallels, equator, prime meridian

Facts about Lines of Longitude--Are known as meridians.--Run in a north-south direction.--Measure distance east or west of the prime meridian.--Are farthest apart at the equator and meet at the poles.--Cross the equator at rightangles.--Lie in planes tha

Why is 1:24,000 scale referred to as 7.5 minutes?  These maps cover a 4-sided area which is divided into quadrangles bounded by two lines of longitude high and two lines of latitude wide. A 7.5-minute map shows an area that spans 7.5 minutes of latitude and 7.5 minutes of longitude (7.5 minutes x 1.15 miles = 8.625 miles, where 60 minutes equals one degree of angle.

Map Legends, Symbols and other Details

Look closely at the map legend. It’s loaded with map-reading clues and navigational data. Start by studying what each line, symbol and color means. Generally, green indicates denser vegetation, while light or colorless areas suggest open terrain. And, as you’d expect, streams and lakes are shown in blue.

The legend also lists key data like the map’s scale, contour- and index-line intervals, grid systems (used for more advanced navigation) and magnetic declination (needed to set up your compass).

USGS Topographic Symbols

Resources

  • Mighty Hatchet Map Section
  • USGS Maps: US Topo maps can be downloaded free of charge from several USGS websites. All maps can be viewed and printed with Adobe Reader or comparable PDF viewing software. Limited GIS functionality, such as displaying ground coordinates, is available with all maps, and the layered construction of the PDF files allows users to turn data layers on and off.
  • Magnetic Field Calculator
  • Magnetic Declination Map Finder

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