Even though GPS receivers are mass produced, you can customize how they work with GPS accessories and options. Choosing the right options when you buy a receiver or when you add accessories can make the difference between having a tool you use or owning an expensive paperweight.

Choosing Your Best GPS Options
How you plan to use your GPS unit determines which options make the most sense. For instance, if you want to use the GPS device for boating, a waterproof case is a must. And if the receiver also floated, that would be a bonus.

• Basic tracking features: storage for waypoints (path reference markers), routes (set of waypoints), and the track log (record of route traveled). The longer or more complex your planned routes, the larger your storage requirements. Check both how many waypoints per route and the number of routes the GPS unit will store. Also, some GPS receivers give you more options for identifying waypoints with names, symbols, and comments.
• Electronic maps. Basic GPS devices have no mapping capability, intermediate units have a basemap (built in and permanent), and advanced receivers have memory to load maps of your choice. The basemap is typically a large area map lacking in detail. It may be sufficient for interstate highway travel, but not for city or water navigation. For advanced units, GPS makers offer a variety of highly detailed maps downloaded from online or a CD. Maps are transferred from a computer connected to the GPS device with an interface cable. Some GPS units use removable memory cards instead of internal memory for map storage. The more memory the GPS receiver or memory card has, the larger and more detailed the map stored can be. You'll usually want 16 MB or more of map storage memory.
• Location accuracy. If maximum position accuracy is a requirement, you'll want GPS units that are Differential GPS (DGPS) or Wide Area Augmentation System (WAAS) capable. WAAS is preferred, since it doesn't require the use of another receiver as DGPS does. Receivers with an external antenna hookup let you use an auxiliary antenna for better reception and improved accuracy. And to keep you on track, you may want a unit that has an audible alarm to signal when you've gone off course.
• The display. The size of a GPS display can never be too big, especially if you're trying to read it when traveling in a vehicle. And for most situations, a color display makes for easier map reading. However, color displays not only cost more than a grayscale display, but they also go through batteries more quickly. For viewing at night, the display should have backlighting and preferably the keypad too.
• Miscellaneous features. A universally handy feature for GPS devices is a built-in electronic compass. It lets you know your heading even when you're not moving. And if you need more accurate altitude readings, get a unit equipped with a barometric altimeter. The barometric sensor can show your elevation as well as pressure reading variations to help detect weather changes. Boaters may want such features as tide prediction tables and loran formatting capability. Flyers might choose a GPS receiver that gives them their glide ratio and vertical speed.

Choosing GPS Accessories
A must-have accessory for vehicle use is a secure GPS mount. It makes reading a handheld receiver easier and keeps both your hands free. You can get mounting brackets for the dash, windscreen, and even a trail bike handlebar. Another good accessory for vehicle use is an external GPS antenna for getting optimum satellite signal reception. Keep in mind, if you can't see through it, GPS radio waves won't penetrate it. So if you're flush-mounting a receiver in a an instrument panel, a remote antenna will be required. GPS receivers powered by internal batteries can usually run off a vehicle's battery with either a special power cable or an adapter that plus into the cigarette lighter. And rechargeable batteries with a recharger can also cut down on replacement costs

Software and a computer let you transfer maps to a GPS unit as well as speeding up the route making process. There's software available from both the GPS makers and independent sources that let you create and edit trip information on a computer and load it into your GPS receiver. An even faster method of route creation is done with autorouting. Autorouting lets you choose a destination and a turn-by-turn route from your location is automatically calculated and displayed on a map. GPS receivers and software with autorouting may also have voice prompts to guide you at each turn.