A larger number of satellites will allow accurate positioning at almost any place on earth. eg the new German road toll system based on GPS, to settle accounts of commutes. With GPS you can do even more. Here are some links to interesting sites

Here you will find Schematic Circuit Diagram for DIY and further information on GPS Global Positioning System
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APRS GPS receiver system fuee Displays the current position of a transmitter on the PC monitor	au.geocities.com/vk3hjq/vk3hjq/aprs.htm
GPS cable for connection to PC build yourself, various manufacturers	www.gpsy.com/cables/making.html
GPS synchronized frequency standard. Contains some very interesting basics!	www.rt66.com/~shera/QST_GPS.pdf