Choosing a Handheld GPS

You need to think carefully about buying a handheld GPS. The wrong decision could put you in danger. You should have a navigator for those backwoods excursions, but you need to know how to use it and what it will and won't do to be sure you're operating safely.

Types of GPS
A handheld GPS navigation system locates your position by sending a radio signal to orbiting satellites. The satellites return the signal, and by measuring and comparing the distance from three or more of them, your position is triangulated within a small margin of error. GPS systems that can talk to more than three satellites provide a more precise read of your position.

Handheld GPS units differ from car GPS navigation systems in a few ways.

They're smaller. Designed for portability, handheld GPS systems are lighter and smaller than car models. They have smaller screens that must be held closer to the eye to read, and they have fewer programmable functions.

Their transmitters are less powerful. Cheap GPS handheld receivers have much weaker transmitters. This means that thick foliage can block satellite signals, preventing the device from working.

They run on batteries. Auto GPS runs off a vehicle's power system and works as long as the car has power. Handheld GPS fails if the batteries die.

Looking at these differences starts to bring the safety issues into focus. Here is where you need to think about what you'll be doing. If you're hiking well-known, marked trails and just want to see your altitude or distance traveled, a budget handheld GPS will do. The further you get from civilization, the more you need reliable, accurate features that can help you find your way back or signal rescuers in case you get stuck.

Hybrid auto and handheld GPS navigation systems are starting to appear on the market. These are larger and more battery-hungry than dedicated handhelds. They're great for camping and daytrips, and the stronger transmitters have some usefulness in backcountry situations, but their size and battery consumption need to be taken into account before you head off trail with them.

Display Types
There are several display options to choose from with handheld GPS units. The most user-friendly is a flat map, similar to the maps you'll find in car GPS navigation. Each GPS unit comes with a built-in basemap that shows major features, but to get the most from the unit you'll want to have additional regional maps that show local roads and features. Some handheld GPS systems can download free maps from the Web, while others can only use maps that you buy from the manufacturer.

The most basic GPS units, such as the wrist-sized Garmin Forerunner and Garmin Edge, don't have a map display but instead provide your latitude and longitude, which you then need to correlate to a map. These GPS systems can also include a compass, altimeter and distance calculators. Those who are experienced navigators won't mind the lack of a map, and these units provide enough information for you to be located in the event of an emergency.

At the high end, hikers and climbers will want to consider handheld GPS navigators that provide topological maps. This gives you a three-dimensional view of the trail ahead, based on satellite imagery and measurements.

If you're heading deep into the backcountry, know the type of display that's best for you, and what information you need to have. Look for a high-contrast display that won't get washed out in bright sunlight. Although color displays are common, black-and-white displays are often easier to read.

Treat a handheld GPS as you would any other piece of safety equipment. Be sure the screen is large enough for you to read, and make sure that it's easy to access and understand the device's functions. Large, well-spaced buttons that are clearly labeled will be the simplest to use in extreme cold or if you're injured.

The SiRFstar III chipset is the most highly recommended technology for transmitting and receiving data. This advanced chipset powers up more quickly in cold conditions and is less prone to interference from thick foliage. It also has a faster TTFF (time to first fix), which is the time it takes for the GPS to locate and communicate with satellites. As an added bonus, SiRFstar III handheld GPS systems work better in areas with tall buildings, in case you want to explore closer to home. You won't find this chipset in bargain GPS handheld units. Look for a receiver system with a minimum of 12 channels and try to get more, as a greater number of channels reduces the interference caused by trees and rocks.

Another way to boost GPS accuracy and transmission, with or without SiRFstar III, is to look for Wide Area Augmentation System (WAAS). This system supplements satellite signals by correcting them through 25 ground stations located in the United States and Hawaii. If you're in range of a WAAS station, you'll receive the signal, and the difference between a WAAS result and a satellite result can be significant. WAAS positioning is required by US Government regulations to be within 7.5 meters of your actual location 95% of the time. In practice, WAAS has been found to be accurate within 1.5 meters, compared with 50 meters for satellite-only GPS in some areas. Adventurous explorers dealing with potentially hazardous terrain will want the extra accuracy of a WAAS-enabled handheld GPS.

Features to Consider
A handheld GPS has a challenging life bouncing around in outdoor extremes. Look for a hard outer casing and shock absorbers that protect the electronics inside from damage.

It's good to have a waterproof casing as well. Look for waterproof, not weatherproof, which won't save the GPS if it's submerged. The International Electrotechnical Commission has developed a scale that measures the water resistance of electronics cases, ranging from IPX0, which provides no water resistance, to IPX8, which can be continually submerged. A rating of IPX4 or higher is recommended for handheld GPS navigation, as this provides protection against brief periods of submersion or heavy rains.

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