Obviously the first thing to consider when buying a gps system is how you are going to use it. There are basically two major uses of gps systems, hand held(outdoor) use and in car use. Generally when using a hand held GPS for hiking and geocaching, coordinates are programmed into the hand held machine which then tells you which direction you are supposed to go and how far away you are. Most car navigation systems are not designed for this capability.
Features to look for car navigation systems:
- Large display
- Street mapping
- A computer interface
If you plan on using your GPS to navigate while driving in your car, its weight is not nearly as important as its ability to display street maps.
Recommendations for Car Navigation Systems
Features to look for hand held systems:
- Weather proofing
- 12 receiver channels
- WAAS (Wide Area Augmentation System)
- Topographical mapping
- Back tracking
WAAS greatly increases the accuracy of your GPS, in most cases to within 10 feet. Accuracy within a few meters is important for the outdoor enthusiast but not nearly as important for navigating through town in your rental car. Next, be sure your GPS has at least 12 channels of reception too. Since your GPS will only work when it receives signals from satellites orbiting the Earth, less than 12 receiving channels will not get the job done in wooded areas or in steep terrain.
Recommendations for Hand Held Systems :
Excerts from treeblog