There are more than 1,300 geocaches in Traverse City's two main Zip Code areas - 49684 and 49686. Geocaching is an adventure game for people with GPS (Global Positioning System) devices. These are small handheld electronic devices that use satellite transmissions to locate exact positions on the ground. They are the modern equivalent of a compass. Participating in a geocache hunt is a good way to make a game out of owning a GPS unit. Individuals and organizations all over the world have set up caches, which can be simply a log book or a variety of different items. Whoever sets up a cache places the GPS coordinates on a worldwide Web site, www.geocaching.com, and others use those coordinates to try and find the cache. Once found, a cache may provide the visitor with a variety of rewards, ranging from comic books to postcards to whatever. Generally, if a participant takes something out of the cache, he or she is expected to leave something else in its place.