Understanding GPS: A Buyer's Guide to GPS

Overview

The primary function of consumer-end handheld GPS units is to pinpoint your location on the face of the earth, and display through maps your distance to a desired destination. Many people can find convenience in owning a GPS unit. One of the more common places where they can be used is someone's vehicle, for navigational directions. Especially for off-road traveling, where both the terrain and road may be unfamiliar to you, or where overhead direction signs are scarce. For many, it sure beats humongous car maps that never seem to fold back into their normal positions, or rolling down windows and asking for directions in a strange town.

Handheld global positioning devices can be used for a number of other reasons too. People in aviation and boating also use GPS units for finding locations. If you plan to take a fishing trip, handheld GPS units will help you while you're out in the waters.

Handheld GPS units come with various capabilities. Most fit into the palm of your hand, and have a thick but short antenna. They all have some sort of display screen, which come in various resolutions and are usually backlit. Some units have an internal memory from which you can access a Map Database, displaying major roads and highways, cities and other navigable details. More advanced units will even allow you to load onto your device more comprehensive street detail, via an additional Flash memory. Many GPS navigators will also provide you with additional information like distance, bearing, speed, time to go, elevations and more. All units work on a rechargeable battery.

To pinpoint your position on the earth, and your distance from your desired destination, all GPS units use some type of channel tracking system. The more satellites needed or used to track your location, the more accurate the reading. Average handheld units will track using 3 satellites, while higher end units can track using up to 12 satellites, and can usually track very well even in the toughest weather conditions.

Storing Locations

One of the major advantages to GPS units is that they have the ability to store specific locations or landmarks, so that they are always remembered. Most units can store hundreds of locations, which are sometimes referred to as "waypoints", including routes and legs or branches off these routes.

Some GPS units may have a slot for optional software modules that already have pre-programmed landmarks and maps of particular regions. When this is possible, it may prove to be extremely beneficial when exploring unfamiliar areas in foreign places.

How They Work

Your GPS receiver requires signals from at least three satellites to determine your unique position on earth. With a fourth signal your altitude can also be determined. Receiving signals from more than four different satellites, the position of the GPS receiver can more accurately be determined. Cheaper models can track with only three satellites, while high-priced units can track with up to 12.

Longitude & Latitude

Locations and waypoints are located and stored using longitudes and latitudes. With these two measurements, you can identify any location on the face of the earth. They are both measured in units of degrees. Latitudes vary from 0 degrees at the equator to 90 degrees to the north and south poles. Longitude varies from 0 degrees at Greenwich to 180 degrees East and West.

Accuracy

Due to many factors in the earth's atmosphere and environment, all GPS units have a probability of error, a possible level of inaccuracy. The factors that may contribute to this can be environmental changes in the earth's Ionosphere, extremely adverse weather conditions, signals from satellites getting bounced off mountains (or other objects) and being sent distorted, or even computational errors. Horizontally, allow for a level of error between 2 and 7 meters, and vertically between 60 and 100 meters with most handheld GPS units.

Additional Features

Depending on what model GPS unit you'll be getting, it may come with a number of various features that will help you navigate your way through anything. A technology commonly referred to as Northfinder tells you where the sun and moon are depending on where you are and the direction in which you are standing. Some units can also project how long it will take you to get to your desired location from where you are now.

Some GPS units can accept accessory modules that cover a particular region that you may be traveling in. These modules can provide certain local landmarks, road maps, and terrain guides that can help you through specific areas.

Battery

Most handheld GPS Units operate using standard alkaline batteries (usually AA). Units can operate on this battery power for anywhere from 15-30 hours, depending on specific model and the frequency of use. Many devices also have an extra internal battery, often a flat Lithium cell, which can last for one or more years. This extra internal battery helps retain the memory of the waypoints you've entered into your device. The Lithium battery may not be used to operate the GPS device.

Other GPS Products

There are a number of GPS hardware and software products that can work with your portable computer or Palm device. If you're seeking compactness and focused functionality, standalone handheld GPS devices may be just what you're looking for.

GPS Fees or Free

GPS is operated by the United States Government and is provided free. There is no charge for using GPS with any dedicated receiver (ie. Garmin, Magellan). Cellular Phones and wireless PDA units that have GPS capabilities may be charged a monthly fee for use by the wireless service carrier (ie, Sprint, ATT). You may wish to consult with your wireless carrier regarding any possible fees.

Buyer's GUIDE:

Please refer to our guide: Buyer's Guide: What to look for before buying a GPS unit?