1. The USA invented the GPS in the 1970s.

2. Anyone can use it to find out exactly their locations and track their movement.

3. GPS provides information on your speed and direction by tracking your position over time. For GPS to work, your smartphone must be in contact with four or more satellites in space. Then it uses the data to calculate the exact time and position on Earth.

4. Four things explorers must carry to survive are a compass, torch, map, and smartphone with GPS.