GPS Game : Where Am I?

A Global Positioning Satellite (GPS) receiver:

1. Picks up radio signals from a satellite.
2. It uses information in those radio signals to:
   1. find the satellites' locations
   2. find out how far away the satellites are
3. Finally, the receiver uses the satellite locations and distances to calculate its own location on Earth.

In this interactive game, students are presented with four satellites which are shown in orbit over a map of Nubia. For each satellite, a distance is provided (e.g. 2118 km away) which indicates how far the satellite is from the GPS receiver. The object is to use the distances from the satellites to determine where the GPS receiver is as accurately as possible.

At first, students are asked to estimate the location of the GPS receiver. After making an estimate, the game provides a line from each satellite that extends the distance that the satellite is from the receiver. With one end of the line fixed on the satellite's location, the line can be rotated around the satellite to create a circle with a radius that is the distance from the satellite to the GPS receiver. For each satellite, the GPS receiver can be located at any point on the circle.

When circles are drawn around two satellites, there are up to two locations where the circle lines intersect. Now the location of the GPS receiver is narrowed to these two locations.

When circles are drawn around the third or fourth satellites, the number of possible locations is reduced to one and the actual location of the satellite is revealed.