The letters GPS stand for Global Positioning Device. Vehicle GPS devices connect to several satellites at a time. The satellites are located in the space. A GPS unit then uses information received from satellites to identify its location.
GPS location sensor needs to be connected to at least 3 satellites to identify its latitude and longitude and track movement. With a connection to four or more satellites, a sensor can determine its altitude in addition to its latitude and longitude. Signals from GPS satellites travel to a vehicle GPS system at the speed of light. A GPS system intercepts these signals. Next, it measures how long it took for a signal to get to the sensor. Then it calculates how far away the sensor is from each satellite and identifies location.
Initially the GPS satellites were placed in space by the US Department of Defense for military purposes. An early satellite-based system named TRANSIT was operating in the 1960s. More refined versions with multiple satellites were in use by general military in early 1980s.
Also in 1980s the US Government made the satellites available for civilian use. However, the military was using interference signals to make sure that it was the only one who could use the system with precision. President Clinton created a law in 2000 prohibiting the military from using interference. This immediately made civilian GPS systems more accurate.
When first civilian vehicle GPS devices became available, they were expensive, big in size, oftentimes needed an external antenna and a power source.
Nowadays GPS systems are much different. They are usually very small in size and fast in operation, yet they have much bigger screens compared to 10 or even 5 years ago. They have a built-in antenna and a built-in battery, meaning that a GPS does not need to be connected to an external power source during operation.
Modern car GPS systems are also much more than simply a GPS location platform. They have Bluetooth capabilities for hands-free calling using a smartphone. They have libraries with maps, points of interest and all kinds of voice-enabled tour guides, from location based to interest based. Location based tour guides may offer a tour of a certain city or state. Interest-based guides can take a traveler across different states offering to visit various Greek Churches or abandoned coal mines.
Early GPS systems could only tell latitude and longitude. Modern GPS with real-directions use street names when directing drivers where to go and show distances and places of interest on the screen.
There are also apps for smartphones available in Apple Store and Android market that significantly expand car GPS features. For example, an app called Smartlink syncs with car GPS through Bluetooth and gives users access to the contact book of their phone without having to type information into GPS.