Turkey

A Car GPS navigation system lets you know exactly where your car is at any time. It uses Global Positioning System (GPS) satellites, which communicates with an in-car sensor via radio signal. The in-car GPS sensor receives the signal from the satellite and compares it to how long it takes the signal to arrive. From that it can calculate the distance to the satellite by knowing the radio signal speed.
When you drive with a car GPS navigation system, you use the position of three GPS satellites to calculate the position of your car on the land. A fourth satellite is needed to calculate the distance to the satellite by knowing how long it takes a radio signal to get there.