How many types of GPS systems are there?

Related questions

1. How does Google satellite get its images?
2. Do planes have transmissions?
3. Does Google have their own satellite?
4. What are the three basic segments of the GPS system?
5. Is GPS time accurate?
6. Do pilots use GPS?
7. Do planes use GPS?
8. How accurate is military GPS?
9. What is Raim GPS?
10. How do planes see at night?

Tags

1. #easily
2. #types
3. #trackers
4. #vehicles
5. #other
6. #monitor
7. #there
8. #while
9. #instance
10. #tracking
11. #people