Hopefully, we can "clear the fog" surrounding GPS units and help you understand their uses and technology.   

Handheld GPS Uses

One of the first things you need to ask yourself before buying a GPS unit is, "What will I use it for?" Are you a weekend angler, an occasional hiker, or a serious big-game hunter backpacking into unknown territory? A lot of these factors determine the type of GPS unit you should purchase. The outdoor enthusiast that will use a GPS occasionally won't need a lot of waypoints or "storage" for their GPS unit. On the other hand, someone that does a lot of fishing or hunting and wants to "mark" spots, or find base camp through a set "route" will need a GPS unit with more storage and better functions. 

Smaller, more economical units aren't necessarily less accurate than their more expensive counterparts, but they usually have fewer features. These inexpensive units typically come with minimal built-in maps, instead relying on user-defined waypoints for navigation. For example, you can create a waypoint at the boat ramp, leave the GPS on as you cruise the lake, and set additional waypoints at various points of interest along the way. Then you can use the GPS to find your way to any of the waypoints you established. This is basically called "leaving a breadcrumb trail." Some units built for camping and backpacking even come with elevation points, so you get more "3-D" waypoints. Another difference you'll find is that more expensive units have the ability to automatically set a "breadcrumb trail" and also have the ability to store more waypoints.  

For travel in a car, you'll want a GPS with more detail and the best possible built-in maps. A unit that accepts memory upgrades and links to a computer is also desirable.

Hiking units can be adequate for boating, but there are many specialized marine GPS devices that are much more suited to hitting the water. Some have fish finders, sounding equipment, and charts that contain more detailed lakes and coastline information than units meant for driving. The best units also provide information about maritime navigation aids like buoys as well as about known hazards.

GPS Accuracy

Electronics entered the world of navigation in the 1930's with the use of radio beacons to signal planes toward airfields. In the 1960's, the loran (Long Range Aid to Navigation) system was established. It worked by timing signals received from different LORAN transmitter stations. It was replaced later in the 60's with the Omega System, which provided worldwide coverage.

NAVSAT (NAVigation SATellite system) or better known as TRANSIT was built in the late 60's and was the first operational satellite navigational system.  Utilizing six satellites, the TRANSIT posted new information every 90 minutes and was used until 1996.

Finally we enter the world of GPS (Global Positioning System).  In 1978, satellites were launched into space. In 1989, second generation satellites (Block II) were put in orbit to bring a grand total of more than 24 GPS satellites in space. In 1983, President Ronald Reagan issued a directive that made GPS transmissions free of charge to all after a Korean airplane went down that could have been saved with proper navigational tools. 

The system became fully operational in 1995, but the units still weren't as accurate as they could have been because of time errors that were inserted into the system by the government in the original satellites.  But in May 2000 these errors were taken out so that civilians can have the accuracy that the military's GPS units have. Good units can now pinpoint an area to within a few meters. The elimination of the government restrictions on GPS accuracy has greatly improved the preciseness of GPS units.

Some units can be even more accurate with additional hardware that makes them compatible with Differential GPS signals (DGPS) which increase accuracy to within a few feet. This is especially helpful for boaters, "geocachers," and people needing their GPS units to have pinpoint accuracy. Unfortunately, the extra receiver needed to pull in DGPS signals can be expensive and bulky, considering the signals themselves are still not available in many areas.

Moving-Map Displays

Nearly every GPS sold today has a moving-map display, which is great for use while driving. These displays show your position in the middle of the screen while the map scrolls underneath your position marker as you move. This ensures that the maximum amount of surrounding map data will always be displayed. 

Display

When purchasing your GPS, the key is resolution over screen size. Resolution is the maximum number of individual dots (called pixels) that fill the screen both horizontally and vertically. A resolution of 120 x 160, for example, means the unit can display a maximum of 120 pixels across, 160 pixels down, with a maximum of 19,200 pixels on the entire screen. The more pixels per inch, the higher the resolution. 

The size of the screen and the amount of pixels will also limit the amount of "map detail" you will have. The higher-end units will show a lot more detail than more economical units. Just remember that large screens may make the GPS unit larger and will probably use up more battery power.   

Some of the newer handheld GPS units on the market sport screens capable of displaying 16 or more colors at once. While this makes maps easier to read, it sacrifices battery life.

Reception

There are 24 GPS satellites orbiting the earth at any given time, and most handheld receivers sold today can track up to 12 of these at once (they're called 12-channel receivers). GPS signals are relatively weak, and your GPS has to lock on to at least three satellites before it can provide any useful information. Four or more satellite lock-ons are required to add accurate elevation data. Another term you will come across when shopping for a GPS unit is "12 Parallel Channel Receiver." Don't worry yourself with this phrase because most all recreational GPS units are 12 channels, and the "Parallel" just indicates that the receiver tracks more than one satellite simultaneously.  This is basically a necessity for a GPS unit to work because it takes at least 2-3 satellites to get a reading. 

Another thing to consider about GPS units is that their signal can be weakened by thick tree cover or other overhead obstructions. The GPS unit must have a "line of sight" to get a signal. Fortunately, most units are quick to re-acquire the satellites once a clear path is established.

Like a computer, a GPS unit can only hold a set amount of information, but some models can accept memory upgrades that greatly expand their functionality. With an 8 MB (megabyte) or 16 MB memory cartridge in a GPS unit, the device can hold many times the number of maps as it previously could.

Most of the units available on today's market are preloaded with data, but most are blank and must be filled via a computer connection. Keep this in mind when purchasing a GPS because it can explain price differences between similar units.

Computer interfaces are good for more than just downloading better maps. Most manufacturers occasionally update the software that powers a GPS unit (called firmware), and the only way to get the updates is to attach your GPS to your computer to download the patches. Updates correct problems with existing features and sometimes add entirely new features to the GPS.

Water resistance ratings

Unfortunately, you're not going to find many waterproof GPS units. Some do have a certain amount of water resistance. If you plan to use your GPS in a rugged environment or while boating, look for units with an IPX7 rating, meaning they are designed to be able to sit in a depth of 3 feet of water for up to 30 minutes. An IPX4 rating applies to devices that are not sealed as well but still should be able to shrug off a rainstorm as long as they are not fully immersed. GPS devices with an IPX2 rating are better left in the car; they are rated to withstand only a light misting, and larger amounts of water will seep into the unit, possibly damaging it.

Tracks vs. Routes

Tracks and routes are not the same thing. Nearly every GPS can track your movements, leaving a "bread crumb" trail (the waypoints) so you can see where you have been. As we discussed before, cheaper units force you to backtrack manually, while more capable devices have a "track back" feature that will point you in the right direction as you follow the original route in reverse. They also will let you save a track so you can use it again later, but the number of tracks you can save will depend on their detail, length, and the memory capacity of your GPS.

Built-in routing features are only found on some of the more expensive GPS units. This feature lets you enter a few waypoints, cities, or other coordinates, and then it creates an efficient route that will take you from one point to the other. Advanced routing features include things like displaying the fastest or shortest route (they are rarely the same) and the ability to create a route from one specific address to another.

A lot of the newer GPS units, and not just the high-end ones, allow you to connect them to your computer for map downloads. There are a lot of different programs on the market that you can fill your GPS unit's memory with.  Investing in better map software is one of the easiest ways to add routing features to an inexpensive GPS.

Conclusion

Hopefully, you've come out of this with a clearer idea of how GPS units work, and what to look for when searching for your perfect unit. If you get confused, find a fishing or hunting buddy that owns a GPS unit and talk to them about what features work best for them, as well as which ones they could do without.   

Click here to view the GPS Glossary of Terms.