Is a GPS Right for Your Adventure?
During the past decade, GPS (global positioning system) devices have become valuable for the casual and serious outdoorsman. And bicyclists, mountain bikers, and hikers have caught the technology bug. So is one right for you?
What is It?
The Global Positioning System was developed by the U.S. military in the late seventies and early eighties. After the U.S. government opened up the system for use by the general public, industry and civilian users have expanded the system into about every areas of life. Free to anyone who has a receiver, the ability to know location, time, and altitude is possible almost anywhere in the world, day and night, and in any weather.
Three components make up the system: 24 satellites orbiting above the world, control and monitoring stations on Earth, and the GPS receivers 
owned by users. If the receiver has contact with at least three of the 24 satellites, then the map coordinate and time will be calculated. A fourth satellite contact will enable the receiver to calculate the altitude of the position.
In basic terms, a receiver locks onto each available satellite's transmission, determines the distance away from each satellite by measuring the time it takes the radio wave to reach the receiver, and calculates its location on Earth by triangulation of the satellites, each in its own orbit. The distance from a fourth satellite enables the receiver to determine its exact position on Earth.
Accuracy and Limitations
GPS can be used in any type of weather, rain or shine, cold or heat, snow or ice. However, some conditions can affect a receiver's usefulness: heavy tree cover, cliffs, canyons, tall buildings, steep mountains, and other locations that limit the radio signals from at least three satellite. If you find yourself in any of these conditions, you can relocate yourself away from the obstructions and the GPS receiver should calculate your location.
Some receiver units have better reception than others. Reception can be enhanced with different antennas configurations or with the addition of a high-sensitivity processor chip, such as the SiRF Star III. Some of the typical antenna configurations include:
- The Quad helix antenna is the most common on current models. It resembles a spiral configuration that can be enclosed by an outside cover or within the unit itself. This antenna seems to works well under heavy tree cover.
- The Flat patch is a less expensive alternative to the quad helix antenna. It seems to work well in open country.
- High-sensitivity processor chips allow enhanced position accuracy even in canyons and deep tree cover no matter which antenna the unit uses.
- Built-in antennas are less likely to get damaged, but can't be repositioned to improve reception.
- A WAAS-enabled GPS unit can achieve position accuracy of better than three meters under ideal conditions. This is particularly true if the unit has a high-sensitivity processor chip.
- Optional plug-in antennas, common on models for cars and boats, enable a unit's antenna to be relocated.
In general, you can expect a map coordinate accuracy within 20 feet and worst for altitude. I know that a lot of the units advertise 10 feet accuracy, but this precision would be under ideal weather conditions. Unless your unit is equipped with a high-sensitivity processor chip (e.g., SiRF III), do not expect an accuracy of 10 feet or less on a regular basis.
Some GPS receivers have a barometric altimeter incorporated into the unit. This altimeter operates separately from the satellite information and can improve the accuracy of the altimeter measurement. In addition, the barometric altimeter can inform you about changes in weather.
Basic Functions
In the nineties, civilian GPS receivers were designed to cater to almost anyone. Fortunately, as popularity gained momentum and users needed specific capabilities, receivers were design to excel in certain fields: hiking, biking, boating, car traveling, and so on. Consequently, not every receiver will satisfy everyone. You need to know what each receiver can do, how it is going to do it, and in what environment it will function.
Anyone who is using a GPS receiver to follow a mapped out route or to find out a location must understand three principals:
- Waypoint: A waypoint is a point of reference or checkpoint on the map. Some examples include a trail head, an intersection, a rest stop, and so on. Waypoints are usually created and saved in the receiver's memory before leaving on a trip, or they are created in the field at a place whose location you want to record. Sometimes a series of waypoints are sequentially linked in order to form a route. On the receiver's map screen, a waypoint is denoted with an icon. As you are moving along your route, you can see your current position in relation to the waypoint.
- Route: A route is a series of waypoints that define the intended path of travel.
Usually, you decide on a way for getting from one point to another, and then create a route in the unit by inputing a series of waypoints in the popular sequence. The maximum number of waypoints that can go into a route varies among GPS units.
- Tracks: A track is a series of point along the route that you have traveled. It is like leaving 'breadcrumbs' as you travel. A track allows you to reverse course and retrace your path of travel. If you get lost, then you can find your way back. In order to do this reverse track, you will need to keep the unit on at all times. Typically, on a GPS map screen you will see a line denoting the track of your travel and an icon showing your current position. Large tracks will take up a fair amount of a GPS unit's memory. Some GPS programs will take a track made up of hundreds of locations, and collapse it into a route with only several tens of location points. This feature uses less memory, but gives less detail.