What is GPS?
GPS or Global Positioning System is a system of satellites created and maintained by the U.S. Department of Defense and used for worldwide navigation. The GPS project began in the late 1970s for the military but was deregulated for public use in the 1980s. At any given time, there are 24 GPS satellites orbiting the Earth transmitting high frequency radio waves back to the surface. Each satellite orbits the Earth twice in one day and is monitored by terrestrial control stations. This network of control stations, called WAAS or Wide Area Augmentation System, was initiated by the U.S. Federal Aviation Administration to increase the accuracy of global positioning. An additional feature of GPS called DGPS or Differential GPS was incorporated by the U.S. Coast Guard for precision marine navigation.

Garmin iQue 3600 Handheld GPS Receiver

GPS is free to the public and doesn't require any initial set up charges. To access the system, you need a GPS receiver to translate the code to geographical information. Due to security issues, GPS operates on two different types of code–C/A Code (Coarse/Aquisition Code) and P-code (Precise Code). The C/A Code is for public use and is less accurate than encrypted P-code for military use. Generally, GPS signals are limited in that they lack the ability to pass through buildings or underground.

GPS Technology at Work
Opening GPS to the public has created a market surge of GPS compatible devices for consumer use. In addition to GPS receivers, many personal electronics such as cellular phones, PDAs, and automotive navigation systems utilize GPS technology. Software packages with GPS locators are also available to convert your personal computer into a GPS receiver.

Calculating locations by a triangulation method, GPS receivers map a 2D position (latitude and longitude) from at least three satellite signals and a 3D position (latitude, longitude and altitude) with four or more satellites. Incorporated with WAAS, a location can be determined within three meters versus a hundred meters via satellite alone.

How information from a GPS receiver is displayed varies among devices. Some units have color LED screens for detailed street and terrain maps while others only use a plotter system to track a route. If you are investing in a GPS device, here are some recommended features to look for:

Lowrance iWay 500c GPS System

1. WAAS Capability. A GPS device that utilizes WAAS increases the accuracy of your location to three meters.
2. DGPS. This feature will increase navigation coordinates over water.
3. Voice Guidance. For automotive use, this is an important safety feature for navigation.
4. Multi-channel design. The new parallel multi-channel standard in GPS receivers are more reliable when maintaining multiple signals to pinpoint a location versus using a single-channel.
5. Compass. Location data should display the differences between True North (North Pole) and Magnetic North (varies with terrestrial shifts) for better accuracy.
6. Map views. From street maps to topographical maps, choose a GPS receiver that displays information relative to its primary use.

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