GPS Information

Let's cover some basic GPS Information.

What is GPS?

GPS stands for Global Positioning System.  It is a world wide radio navigation system developed by the United States Department of Defense.

It employs 24 satellites in orbit around the earth to allow a person to use a GPS receiver to determine her/his position.

How does it work?

GPS uses the principle of "triangulation" to locate points. Triangulation is the idea of knowing the location of two fixed points and the angles from those two fixed points to a third point thus forming a triangle.  Using simple geometry and trigonometry, the location of the third point can be calculated.

A good example of triangulation is being out in a boat and finding a great fishing spot.  You want to come back to this same spot next time so you look on the shoreline and find two landmarks.  You have a compass and you take the compass readings from your spot on the lake to each of the landmarks on the shore.  When you return the next time, if you locate your boat where the landmarks on the shore are at the same compass readings as before, you will be at the same spot on the lake.

The GPS satellites are the fixed points in the GPS navigation system and your location is the unknown point.  The GPS receiver you use contains a program to calculate your position based on where the satellites are located using the principle of triangulation.

History of GPS

Man has been trying for centuries to find a way to determine his location on Earth.

The stars were the first navigation aids man used.  By watching his position in relation to certain stars at certain times of the year and certain times of the night, man could roughly determine his position.

The first navigation tool was the compass.  With it, man could tell in which direction he was traveling, but he could not determine his exact location.

The sextant was the next invention in navigation aids.  It measures the angle of the sun, the moon, and the stars above the horizon.  This gave  the correct latitude, but did not measure longitude.

In 1761, the chronometer was invented.  Sextants could be used in conjunction with the chronometer to measure longitude.

Radio direction finding equipment was invented early in the twentieth century. This type of navigation was restricted by the limitation of radio waves and there were "dead spots" on the planet where no radio coverage existed.

When the USSR launched Sputnik in 1957, the idea of using satellites as "artificial stars" for navigation was conceived.

In 1973, the Department of Defense began a project to build a satellite navigation system.  The first satellite was launched in 1978 and the 24th and last satellite was launched in 1993 giving us what the Department of Defense calls the Navstar Global Positioning System.

This system provides the satellites that all of the GPS units on Earth use to determine position.

Additional GPS Information

Garmin® has created some a very good article containing GPS information at "What is GPS?"

Another excellent source is the U. S. GPS Government website at

End of GPS Information


GPS Information