Introduction to Topographic Maps Banner link to home page GeoSTAC Link to Department of Geosciences at Idaho State University
by Jim Riesterer . . . . . . . . . . Edited by Scott Hughes, Dan Narsavage & Diana Boyack

Topographic Maps Tutorial

Introduction & Materials
What is a Map?
Using Topo Maps
Map Scale
Reference Datum
Map Projections
Distortions
Grid Systems
Geographic
UTM
State Plane
Public Land Survey
Vertical Scale
Creating Profiles
Vertical Exaggeration
Calculating Slope
Using a Compass
Magnetic Declination
Get a Bearing
Go from A to B
Find Self on a Map

Topographic Maps Field Exercises

Exercise 1
Exercise 2
Exercise 3
Exercise 4

GeoSTAC Home

Field Exercises


geostac@gmail.com
April 7, 2008

Get a Bearing

Azimuth Compass

A bearing is a measurement of direction between two points. Bearings are generally given in one of two formats, an azimuth bearing or a quadrant bearing.

An azimuth bearing uses all 360° of a compass to indicate direction. The compass is numbered clockwise with north as 0°, east 90°, south 180°, and west 270°. So a bearing of 42° would be northeast and a bearing of 200° would be southwest, and so on.

For quadrant bearings the compass is divided into four sections, each containing 90°. The two quadrants in the northern half of the compass are numbered from 0° to 90° away from north (clockwise in the east, counterclockwise in the west). In the southern half of the compass, the two quadrants are numbered away from south (counterclockwise in the east, clockwise in the west).

Compass Quadrants

Quadrant bearings are given in the format of N 40°E (northeast), S 26°W (southwest), etc. Whenever you measure a quadrant bearing, it should always be recorded with north or south listed first, followed by the number of degrees away from north or south, and the direction (east or west) away from north or south. In other words, you would never give a quadrant bearing as E 40°N or W 24°S.

Your compass may be an azimuth compass or it may be divided into quadrants. If you have an azimuth compass and are given a quadrant bearing, you’ll have to divide it into quadrants in your head, and the same goes for quadrant compasses if you are given an azimuth bearing.

Measuring a bearing

So, you’re in the field with your map at point A and want to get to point B…how do you accomplish this? The first thing you need to do is determine the bearing from point A to point B. There are two ways to go about this.

protractor on map with compass bearing

The easiest way, is to carry a protractor with you when you’re in the field. If you have a protractor with you, place it on the map so it is oriented parallel to a north-south gridline, with the center of the protractor on point A (or on a line drawn between points A and B). Once you have done this, you can simply read the bearing you need to go off of the protractor.

If you don’t happen to have a protractor with you, you can determine the bearing you need using your compass. To do this, place your compass on the map so that the edge of your compass is oriented parallel to a north-south gridline and the center of your compass is on the line between points A and B.

compass bearing on map

Now rotate the map and compass together until the north arrow on the compass points to 0° on the graduated circle. You can then approximate the bearing you need by estimating where the line between A and B crosses the graduated circle.

It is probably at about this point that, if you are using a Brunton compass (and some others as well), you are probably noticing that the ‘east’ label is on the wrong side of the compass (west of north). You are not hallucinating. It is that way for a reason that will become clear in the next section, hopefully.

 

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