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If you are using a phone this will happen automatically, but some GPS devices need to be manually updated. This will give you the latest information, topography, and directions.  Find the "About" button, usually located in "Settings." Scroll down to see Map Information. If this is more than 6 months old, you will need to update. Plug your GPS into an internet-enabled computer using the cord that came with the unit. Perform an internet search for "your GPS + Map Update" follow the onscreen instructions. There are over 25 satellites orbiting earth that receive signals from your GPS and use those signals to determine your latitude and longitude. Developed by the army, GPS can accurately tell your location anywhere in the world by several feet -- as long as the signal can reach the satellites. Cell phone GPS uses cell towers and internet signals to find your location, so they won't work in the wilderness. GPS needs a clear view of the sky to accurately communicate with the satellite's, so move away from overhangs or tall trees and head outside if you have issues. Generally, if you can see the sky, the GPS can as well. Tunnels, caves, and basements may all keep your GPS from communicating to satellites and working successfully. Most GPS devices are built in Asia, and are used to communicating with satellites over that area. Initializing your GPS acquaints it with your local area. To initialize a GPS, go to "Settings" and click "Initialize." Follow your GPS's manual if you have any problems finding the setting, and know that this may take up to 20 minutes.  Turn your GPS off and restart it if you are having problems. Make sure you have a clear view of the sky. You may need to reset your GPS the first time you buy it by clearing the memory. Refer to the manual for instructions. This is especially useful when hiking. In the parking lot, find your GPS's satellite lock setting and have it get to work -- it usually takes several minutes. Signs that you have a bad signal are changing directions, jittery locations, or error messages. Because a GPS can run out of battery, lose signal, or break, you should never rely on it completely to get around. While useful, you need to be prepared in case you cannot use it for some reason.
Download the latest map updates if your directions are incorrect. Know that GPS uses satellites to locate you. Get into the open. Initialize your GPS when you buy it. Use "Satellite Lock" before you head out. Know that GPS's are not replacements for maps and compasses.