Field Mapping
Name ________________________
The grand tradition of field mapping goes back thousands of years.
All you need is something to measure direction (a compass in our
case) and something to measure distance (like pacing). With these
simple tools, we can map small areas fairly accurately.
Purpose: Become familiar with baselines (closed traverses), techniques for mapping small
areas with simple tools, taking field notes, and plotting a map from field data.
Equipment: provided: magnetic compass, tape measure, protractor, ruler, graph paper, not
provided-bring your own: calculator
Objectives:
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Learn how to use a magnetic compass
Learn the convenient & rapid technique of the “pace and compass traverse” for making
maps in the field
Transfer field data to map format
Definitions
Azimuth: An azimuth is an angular distance from magnetic north measured in a clockwise
direction and expressed in degrees from 0 to 360. When using a magnetic compass to measure
an azimuth, be sure not to use it near metal objects that may disturb the magnetic field.
Closed Traverse: A closed traverse establishes a reference frame, or baseline, on the ground
used to map objects nearby. It is constructed by measuring a series of straight lines, or legs.
All of the legs together are called a traverse. The last of point of the last leg matches to the first
point in the first leg, closing the traverse. Each point in the traverse is called a station.
Location by Radiation: This is another way of fixing the location of objects distant from the
closed traverse. Simply record the azimuth and distance of the object from stations on the
closed traverse.
Pacing: The length of any person’s step (or pace) is quite constant if they walk naturally over
even ground at a normal speed. However, the length of each person’s pace will be different. We
will determine the length of each person's personal pace by walking a measured distance (20
m) while counting the number of steps, repeat, and used then average of the two values. Divide
20 by the average number of paces to obtain your personal average pace length (in meters).
Map Scale: The map scale shows the ratio of distance on the ground to distance on your map.
It is usually expressed as a representative fraction, such as 1:1000
Step 1: Pace Length (meters per pace)
Walk at a normal speed from one end of the tape measure to the other (20 meters) counting
your paces. Record the number in the table. Next, reverse and walk back to the beginning of
the tape measure, counting your paces again. Record the second number. You will then be able
to calculate your average pace length back in the lab.
Table 1: Pace Distance
Distance (m)
Trial 1
20
Trial 2 (return)
20
Paces
meters / Pace
Average
Note: 2 decimal places are more than adequate, and 1 is also acceptable.
Step 2: The Traverse
Our traverse will follow the sidewalk surrounding the Great Lawn. Gather data in the following
way:
1. Sketch the area to be mapped (perhaps on the back of this sheet) and label the sidewalk
corners as Stations A, B, C, D, and E.
2. Begin the traverse at any point. From the first Station, determine the azimuth toward the
second Station and record it. This is called the “foresight.”
3. Walk to the second Station counting your paces as you go, record the number of paces.
(The paces will be later converted into meters back in the lab.)
4. At the second Station, determine the azimuth back to the first Station. This is called
the “backsight.” This measurement is taken as a check on the foresight measured
earlier, it should be approximately 180 degrees opposite.
5. Continue the above procedure for each leg of the sidewalk until you return to where you
started.
NOTE: If the backsight is not close to180 degrees from the foresight, there is a data error and
the foresight should be checked before proceeding. You might have to re-measure the azimuth.
Table 2: Traverse Measurements and Calculations
Traverse Leg
Foresight
Distance
Backsight
(degrees)
(paces)
(degrees)
Ground
Distance
(cm)
(meters)
Station A - Station
B
Station B - Station
C
Station C - Station
D
Station D - Station
E
Station E - Station
A
Map Distance
Step 3: Locate Objects
We will locate several objects for your map using the traverse baseline, including at lease one
corner of a building, at least one tree, and at least one sign using the location by radiation.
To do this, select any tree, sign, or building corner. Walk to the nearest Station and record the
Station letter in the first column. Then, determine the azimuth to the object (using the compass)
and the distance (by pacing).
Repeat this procedure 3 times at least, once for a tree, once for a sign, and once for a building
corner. We will be able to use this information back in the lab to locate on the map.
Table 3: Radiation Measurements and Calculations
Object
Azimuth
Distance
(degrees)
(paces)
Ground
Distance
Map Distance
(cm)
(meters)
Station ____ to Tree
Station ____ to Sign
Station ____ to Corner
Step 4: Calculate Map Distances
In Tables 2 and 3, calculate the actual ground distances by multiplying your pacing length (from
Table 1) by the number of paces between locations. (For example, 70 paces times 0.6 meters per
pace = 42 meters)
Next you will need to convert meters to distances on the map, like we did in the first lab using a
map scale.
For this step, you will need to select a map scale to be used. A good scale for this map is 1:600.
That is, 1 cm on the map represents 600 cm (6 meters) in reality. Simply divide your Ground
Distance by 6 to get map distance in centimeters. (This is a shortcut, normally you would
convert meters to cm by multiplying by 100, then dividing by the map scale of 600)
Step 5: Draw the Map (sidewalk, objects, north arrow, scale)
Draw the closed traverse, and locate the building corners and trees in their correct relative
positions. When locating trees and buildings, put them in the correct location, but use your
imagination when rendering them on the map. In other words, make them recognizable with a little
artwork.
1. Mark a suitable point on the graph paper (provided) to represent Station A. You want
your data to be centered on the paper. Draw a north arrow on the map. Remember,
this is azimuth 0. North is conventionally at the top of the map.
2. Using a protractor and ruler, draw the closed traverse using light pencil marks. When
finished, you will probably notice that there is a “closure gap,” meaning the last point
does not match the first. That is fine, normally we would adjust this by changing each
corner a bit, but in this case leave it as is. This gap tells me that you have faithfully
plotted your data, it will almost never close properly.
3. When finished, darken the lines and label the Stations (A, B, C, D, E)
4. Locate the objects you located by radiation using the proctator and ruler. Use some
artwork to make them recognizable (make the tree look like a tree) and label them.
5. Draw a scale on the map, using a representative fraction.
6. Beautify! (optional)
Step 6: Questions
Hand in your map along with answers to the following questions:
How closely did your backsight measurements match your foresight measurements? What is the
purpose of taking backsights?
How do you think the accuracy of you map could be improved?
MAP