How to Buy In-Car Navigation

So what is GPS and how does it work?

What to Look For

Functionality

• Maps. Most GPS units come either with pre-loaded maps, or come with maps on CD-ROMs that must be transferred to the GPS unit via a computer. Maps are either stored on compact flash cards or on internal or sometimes removable hard drives. Map updates occur every one to three years depending on manufacturer.
• Built-in road maps or street level mapping. Street level mapping is an essential component of an in-vehicle GPS unit. This is a useful feature when visiting new cities, unfamiliar areas, or when looking for a detour route to avoid poor traffic conditions. Some models have all street level maps built-in, others require the user download the maps from a personal computer or laptop via compact flash card or direct USB interface.
• Address to address routing. This is probably the most important feature offered by this type of navigation system. The user inputs the specific address of their destination and the GPS unit will automatically guide the user to that point.
• Route Capability. Also known as automatic destination routing, this feature is available on most models. If you miss a turn while driving, the GPS unit will automatically recalculate your route.
• Turn-by-turn instructions. Some units not only have the ability to route you to your destination, but will also give you turn-by-turn instructions. These instructions are delivered via visual display (arrows), voice command, or both. Voice command is especially nice so the driver does not have take his or her eyes off the road to receive the next driving direction.
• Points of Interest (POI). Along with map information, most units also include handy Points of Interest already loaded in the navigation database. Pre-stored points of interest can include things like restaurants, gas stations, rest stops, amusement parks, lodging, or emergency services. Most in-vehicle units have at least 2 million POI’s to choose from. This can be very handy for road trips or unfamiliar areas when a food or bathroom break is top priority!
• Waypoints. These are user-determined Points of Interest. Not all GPS units have this capability and will only let you route to addresses or pre-determined POI’s. Waypoints allow the user to determine his or her own points-of-interest, by pointing to a destination on the map rather than entering in an address. Some units feature address book storage rather than waypoint storage.
• WAAS Capability. WAAS stands for Wide Area Augmentation System. It a system of ground-based reference stations used to correct errors in GPS signals caused by ionospheric delays, signal reflection, individual satellite clock drift, and other small inaccuracies that can cause the GPS signal to be slightly off. Without WAAS, GPS units have an accuracy of approximately 20 to 40 feet. With WAAS enabled, the accuracy improves to approximately 6 to 10 feet! Currently WAAS is most effective on the east and west coasts, but more WAAS reference stations and satellites are currently being developed.

Technical

• Mounting Options. Mounting methods differ for each manufacturer. Make sure the mounting option included with the unit will work in your particular vehicle. The unit needs to be mounted so that it does not obstruct the view of the road while still maintaining a direct line of sight between the screen and the driver. Most units have options where the GPS unit will mount on top of the dash, clip to the air vents, or mount on a “gooseneck” attached to the windshield via a suction-cup. Some GPS units have other mounting accessories available. Check our Navigation Accessory area to investigate your options.
• Number of Receiver Channels. Today’s GPS units have multiple satellite receivers built-in, each dedicated to a single satellite signal. The more receivers a unit contains translates to a more accurate guidance with fewer tracking “dead spots”. Dead spots are caused by tall buildings blocking the sky, heavy tree coverage, mountain terrain, interfering radio signals, etc. Most of the receivers CarDomain offers feature 12 channel parallel receivers, although some offer even more
• Dead Reckoning or Adjunct Positioning. Some of the higher-end navigation units offer this feature. Dead reckoning is useful in cities or areas where the satellite signal may be degraded by tall buildings. These units contain an acoustical gyroscope that can detect vehicle motions and help track the vehicle’s position on the map until the signal is recovered.
• External Antenna Capable. This can be a useful feature. All automotive GPS units have built-in antennas that work quite well. However, some users may require a stronger signal if their traveling area tends to have a lot of satellite signal obstructions. External antennas guarantee a clear, full view of the sky maximizing possible satellite reception. If your vehicle is equipped with a metalized windshield, then an external antenna is recommended. Metalized windshields can reflect or block satellite signals from passing into the vehicle. Click here to see if your car has a metalized windshield. You can find external antennas in our Navigation Accessories area.
• Screen Size. This is an important factor and as previously discussed, most in-car units come equipped with larger screens than typical handheld GPS receivers. Most in-car units also offer color screens making map detail easier to determine with quick glances. Some units have a photocell built into the back that can sense ambient light levels, automatically dimming the screen into night mode as the day fades into night or changing back into day mode as the night turns into day.
• Data Input. Most units have well thought out user interfaces. Some units use a joy-pad or rocker-pad to navigate through the user menus. Others utilize touchscreen technology taking full advantage of the larger screens and making then very user friendly for in-car use. Touchscreen units usually also allow the use of joy-pad input as well. If mounting the unit somewhat out of the reach is necessary, not to worry! Some units even include remote controls giving the driver or passenger complete control right at their fingertips.
• Memory Availability. Maps are stored either internally on small mobile or removable hard drives (HDD), or stored on Compact Flash(CF) cards. HDD units have enough storage to include points of interest and street level maps for the entire nation (sometimes including parts of Canada and Mexico). If the unit you’re considering uses CF cards, you’ll find most units include a card that is generally sufficient to store street level mapping for a rather large area (usually a few states). As a general rule of thumb, consider a 128MB CF card can store approximately 5 states worth of data, or 4MB per million people. For extra cards or other storage options click into our Navigation Accessories Store!