A topographic map tells you where things

are and how to get to them, whether

you're hiking, biking, hunting, fishing, or

just interested in the world around you.

These maps describe the shape of the

land. They define and locate natural and

manmade features like woodlands, waterways, important buildings, and bridges.

They show the distance between any two

places, and they also show the direction

from one point to another.

Distances and directions take a bit of figuring, but the topography and features of

the land are easy to determine. The topography is shown by contours. These are

imaginary lines that follow the ground

surface at a constant elevation; they are

usually printed in brown, in two thicknesses. The heavier lines are called index

contours, and they are usually marked

with numbers that give the height in feet

or meters. The contour interval, a set difference in elevation between the brown

lines, varies from map to map; its value is

given in the margin of each map. Contour

lines that are close together represent

steep slopes.

Natural and manmade features are represented by colored areas and by a set of

standard symbols on all U.S. Geological

Survey (USGS) topographic maps.

Woodlands, for instance, are shown in a

green tint; waterways, in blue. Buildings

may be shown on the map as black

squares or outlines. Recent changes in an

area may be shown by a purple overprint.

A road may be printed in red or black

solid or dashed lines, depending on its

size and surface. A list of symbols is

available from the Earth Science

Information Center (ESIC).

From Near to Far: Distance

Maps are made to scale; that is, there is a

direct relationship, a ratio, between a unit

of measurement on the map and the actual distance that same unit of measurement represents on the ground. If, for

instance, 1 inch on the map represents 1

mile (which converts to 63,360 inches) on

the ground, the map's scale is 1:63,360.

Below is a listing of the scales at which

some of the more popular USGS maps are

compiled.

A convenient way of representing map

distance is by the use of a graphic scale

bar. Most USGS topographic maps have

scale bars in the map margin that represents distances on the map in miles, feet,

and kilometers. The table below shows

the corresponding area of coverage for

each scale and the linear distance that

each scale represents in inches and 

centimeters.

From Here to There: Determining

Direction

To determine the direction, or bearing,

from one point to another, you need a

compass as well as a map. Most compasses are marked with the four cardinal

points—north, east, south, and west—but

some are marked additionally with the

number of degrees in a circle (360: north

is 0 or 360, east is 90, south is 180, and

west is 270). Both kinds are easy to use

with a little practice. The illustrations on

the reverse side show how to read direction on the map.

One thing to remember is that a compass

does not really point to true north, except

by coincidence in some areas. The compass needle is attracted by magnetic force,

which varies in different parts of the

world and is constantly changing. When

you read north on a compass, you're really

reading the direction of the magnetic

north pole. A diagram in the map margin

will show the difference (declination) at

the center of the map between compass

north (magnetic north indicated by the

MN symbol) and true north (polar north

indicated by the "star" symbol). This diagram also provides the declination

between true north and the orientation of

the Universal Transverse Mercator (UTM)

grid north (indicated by the GN symbol).

The declination diagram is only representational, and true values of the angles of

declination should be taken from the

Finding Your Way with Map and Compass

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 079-99

February 2000

Part of a 7.5-minute topographic map at 1:24,000

scale.

Map area

Map Series Scale 1 inch 1 centimeter (approximate

Name represents represents square miles)

Puerto Rico 7.5-minute 1:20,000 1,667 feet 200 meters 71

7.5-minute 1:24,000 2,000 feet 240 meters 49 to 70

7.5- by 15-minute 1:25,000 2,083 250 meters 98 to 140

(about)

Alaska 1:63,360 1 mile 634 meters 207 to 281

(about)

Intermediate 1:50,000 0.8 mile 500 meters County

(about)

Intermediate 1:100,000 1.6 miles 1 kilometer 1,568 to 2,240

(about)

United States 1:250,000 4 miles 2.5 kilometers 4,580 to 8,669

(about)
numbers provided rather than from the

directional lines. Because the magnetic

declination is computed at the time the

map is made, and because the position of

magnetic north is constantly changing, the

declination factor provided on any given

map may not be current. Contact the

National Geophysical Data Center

(NGDC) to obtain current and historical

magnetic declination information for any

place in the United States. 

NGDC General Information: 303-497-6826

E-mail: info@ngdc.noaa.gov

Web site: http://www.ngdc.noaa.gov/ or

http://www.ngdc.noaa.gov/seg/potfld/

geomag.shtml

Taking a compass bearing from a map: 

(1) Draw a straight line on the map passing through your location and your destination and extending across any one of

the map borders. 

(2) Center the compass where your

drawn line intersects the map border,

align the compass axis N-S or E-W with

the border line, and read on the compass 

circle the true bearing of your drawn line.

Be careful to get the bearing in the correct

sense because a straight line will have

two values 180° apart. Remember north is

0, east is 90, and so on. 

(3) To use this bearing, you must compensate for magnetic declination. If the

MN arrow on the map magnetic declination diagram is to the right of the true

north line, subtract the MN value. If the

arow is to the left of the line, add the

value.

A Word of Caution

Compass readings are also affected by the

presence of iron and steel objects. Be sure

to look out for—and stay away from —

pocket knives, belt buckles, railroad

tracks, trucks, electrical lines, and so forth

when using a compass in the field.

Information

For information on these and other USGS

products and services, call 1-888-ASKUSGS, use the ASK.USGS fax service,

which is available 24 hours a day at 

703-648-4888, or visit the general interest

publications Web site on mapping, geography, and related topics at 

http://mapping.usgs.gov/mac/isb/pubs/

pubslists/index.html.

Please visit the USGS home page at

http://www.usgs.gov/.

(1) Drawing a straight line over the map edge. (2) Reading the compass on the map. (3) Using the magnetic declination diagrams.

If arrow is to the left—add

Magnetic declination diagram

If arrow is to the

right—subtract