The USA invented the Global Positioning System (GPS) in the 1970s. At first, it was a military project, but now anyone can use the system to find out exactly their locations, and (1) their movements.
For GPS to work, your (2) (or 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. However, it is not enough for survival situations (escaping the jungles or deserts) because you must know your direction (which way you are moving) and your (3) (how fast you are moving). GPS provides this information, by tracking your position over time.
For modern explorers, a smartphone and GPS are as important as a compass, torch and map. With the right (4), your smartphone will help you survive.
