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Where Am I? Student Handout 1

View the Geospatial Revolution video and answer the following questions.

1. Give 3 examples of common uses of GPS receivers.

2. What are 2 benefits of this technology of the uses of this technology in emergency situations?

3. Give another example of emergencies where GPS information might be crucial. 

4. How would you use GPS technology in the study of water quality and organism like oysters?
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Where Am I? Student Handout 2

Scavenger Hunt!

You will investigate latitude and longitude coordinates on a USGS map of a small mining town 

near Triumph, Idaho. Copy and paste this site into your browser, or your teacher will provide a 

printed map. http://ngmdb.usgs.gov/maps/TopoView/viewer/#13/43.6501/-114.2636 

The latitude and longitude are displayed at the bottom of the map. 

1. What feature do you find at 43o38’46”N and 114o14’40”W 

2. What feature do you find at 43o38’12”N and 114o14’46”W

3. What feature do you find at 43o39’13”N and 114o15’32”W 

Let’s look at something more local to the Chesapeake Bay. Go to this map,

http://ngmdb.usgs.gov/maps/TopoView/viewer/#11/38.6346/-76.0697

Move/slide the dot at the top of the page all the way to the right so that the map reflects a 2010 

date. 

• You will see the latitude and longitude displayed on the bottom of the map. 

• Click and drag the town of Cambridge to the center of the screen and scroll in to magnify. 

• Click and drag the map so that Cambridge moves to the right of your screen and your map 

is centered on Cornersville. 

• Find the latitude and longitude of these airports. 

4. Rossneck airport

5. Big Oak Farm airport

6. Pokety airport
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WhereAm I? Student Handout 3

Trilateration Activity: How to find a position using GPS

Orbiting the Earth, are a number of Global Positioning System (GPS) satellites that can help 

determine your location on the planet. The concepts behind GPS positioning are very simple, 

but the application and implementation require amazing precision.

GPS positioning works on two basic mathematical concepts. The first is called trilateration, 

which literally means positioning from three distances. The second concept is the relationship 

between distance traveled, rate (speed) of travel, and amount of time spent traveling, or:

Distance = Rate × Time

The first concept, trilateration, is the focus of this activity. It centers around finding your 

position on the Earth by knowing the location of orbiting GPS satellites and the distance from 

those satellites to your location on the planet. However, there is no way to actually take a

yardstick, tape measure, etc., and measure the distance from your location up to the satellites. 

So how can we use trilateration if we cannot physically measure the distances? The answer lies 

in the second concept, relating distance, rate, and time. The trick lies in the fact that GPS 

satellites are always sending out radio signals.

In GPS positioning the rate is how fast the radio signal travels, which is equal to the speed of 

light (299,792,458 meters per second). Time is determined by how long it takes a signal to 

travel from the GPS satellite to a GPS receiver on earth. With a known rate and a known time,

we can solve for the distance between satellite and receiver. Once we have the distance from 

at least 3 satellites, we can determine a 3 dimensional position on the surface of the earth.

Trilateration is determining a position by knowing your distance from at least 3 known points. 

In GPS those known points are the satellites themselves. It is important to understand that this 

is a simple exercise in trilateration itself, and not an exact representation of how the process of 

GPS positioning works. We will be using a flat map and string, when in reality the earth is round 

and the satellites are in the sky, not on the ground. Also, one often can "see" many more than 

three GPS satellites in the sky at any time, so we are going to use four points instead of just 3, 

to exemplify some of the issues surrounding extra satellites. This exercise is a model of how 

GPS positioning works.

This exercise is best completed in groups of 3-4 people.

Materials:

 4 pieces of different color string (pre-cut)
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 Pencil or pen for marking the potential position of each signal

 A large map (provided)

Overview:

In this exercise, we are going to simulate GPS positioning using 4 satellites. You are going to 

pretend to be a GPS receiver somewhere on the map, and will figure out where you are based 

on the 4 "signals" you receive. But for you (and for a GPS receiver), all those signals tell you is 

where the satellite was when it sent the signal, and how long it took for the signal to get from 

the satellite to you. In other words, you have the time elapsed from when the signal left the 

satellite to when it arrived at your location. You also know where the satellite was when it sent 

you the signal, since the positions of the satellites on the map. You need to determine where 

you could be, based on that amount of time elapsed. Since we know the speed of the signal (R), 

and the elapsed time (T), we can figure out the distance (D).

Distance = Rate × Time

In true 3 dimensional GPS positioning, the signals from the satellites are represented by 

spheres. For this exercise, we are going to use circles, since we are on a 2 dimensional map. So, 

as a GPS receiver, you need to figure out just how far from each satellite you are. Keep in mind 

you could be anywhere!

Directions:

1. Lay the provided map flat on your table and tape down all four corners.

2. Get 4 pieces of string, about 1/2 meter long, 1 each of 4 colors. (We need to know how 

far away you are from 4 different points, which are represented by the length of 4 

different colors of string.)

3. Determine exactly how long each string is supposed to be by solving our D = R × T 

equation. The speed of light (R) is 299,792,458 m / s. Use the amount of time that it 

takes for each signal to get from the satellites to the receiver provided below to solve 

for D.

Time for the Signals to reach the GPS receiver:

1. A = .00505783 seconds

2. B = .00423206 seconds

3. C = .00836090 seconds

4. D = .00712225 seconds

Once you have figured out the distance of each of our satellites from our position on the 

ground, proceed to step 4 where you will calculate the scaled distances.
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4. Now you know how long each string is supposed to be, but the distances are a lot longer 

than the strings we cut. You need to account for the scale factor of the map. This map 

has a scale factor of 1:21,283,839. This means that 1 meter on the map equals 

21,283,839 meters on the earth's surface. Using a simple proportion, figure out what 

the scaled version of your string should be. Convert the units to centimeters for easier 

measuring. [Note: In this shorter exercise, the math has been done for you.] The single 

most important thing in this exercise to remember is to make your string lengths as 

accurate as possible, because you are going to be using your string to draw a circle 

showing all the possible places where the satellite signal could have gone in the given 

amount of time. In some cases, the circle may not fit on the paper, and may just show 

up as an arc. You and your team should come up with a way to make those circles and 

arcs as precise as possible. Think about that for a minute before you cut your strings. Is 

there some inventive technique you can come up with to make your circles and arcs 

more precise? Cut your strings and get ready for the next step.

5. Now you have four different strings, representing the distances from 4 satellites. Using 

whatever method you came up with, go ahead and draw your circles and arcs using the 

satellite as the center point. This arc is a representation of where the satellite signal 

would be, given the elapsed time. Remember, our position could be anywhere along 

that arc since that signal is traveling in all directions. Repeat this for String B and Dot B. 

You should see there are at least two places where you could be! What were those two 

places?

6. Complete the process for Strings C and D. You should have a series of arcs and circles 

that overlap in a few places. There should only be one place on the map where they all 

intersect each other. 

In order to know the distance from the satellite to the receiver you need to know 

exactly where the satellite was when it sent its signal. That positional information is 

included in the signal that travels from the satellites. The rate is not exactly the speed of 

SATELLITE A

STRING COLOR

SATELLITE B

STRING COLOR

SATELLITE C

STRING COLOR

SATELLITE D

STRING COLOR

TIME (IN SECONDS) .00505783 .00423206 .00836090 .00712225

DISTANCE (M) 1516299.28784614 1268739.66980348 2506534.7620922 2135196.8339905

SCALED DISTANCE 

(M)

.07124 0.05961 0.11776 0.10032

SCALED DISTANCE 

(CM)

7.12 5.96 11.76 10.03
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light (it's really close though), as there are a variety of things that can cause delays, such 

as atmospheric conditions. There is also the problem of multi-path (signals bouncing off 

the ground or off buildings), dilution of precision (really bad distribution of satellites in 

the sky) and other potential sources of error. For the most part, it really is that simple.

Questions

1. Where did you end up on the map?

2. Why didn't your lines all cross in exactly the same spot?

3. Take a look at how close you came. What would you say your level of accuracy was?

4. How does your accuracy compare to consumer grade GPS receivers or your smart phone? 
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Where Am I? Student Handout 4

Introduction to the Chesapeake Bay watershed

After viewing this introduction to watersheds (https://vimeo.com/14030972) answer the 

following questions.

1. How do we identify a watershed?

2. Why are watersheds important in understanding pollution, flooding, and restoring ecosystem 

habitats in the Chesapeake Bay?

3. What 2 possible strategies can be used to reduce the amount of runoff from heavy rains?

4. Go to http://www.chesapeakebay.net/discover/baywatershed. Identify your watershed by zip 

code. 

5. Your teacher will give you a list of 4 locations around your school yard or building. In a small 

group, find the addresses of these locations using either GPS receivers, smart phones, or this site,

http://www.latlong.net/.

Location Latitude Longitude

1. 

2. 

3

4.