5. Location - "Where am I?"

The first and most obvious application of GPS is to let you know where you are.

GPS is the first positioning system invented to let you know exactly where you are on the planet, in any weather.

Older methods make use of star positions to work out your location but they are pretty useless on cloudy nights!

Knowing the precise location of something, or someone, is especially important when it can be a matter of life and death. For example, when a stranded motorist was lost in a blizzard for 2 days, GPS helped rescuers to find her. Sailors lost at sea are often rescued by making use of GPS.

GPS can not only measure location - it can also measure your height on Earth. This is very handy for measuring things such as the growth of volcanoes. Stick a GPS receiver on the side of an active volcano (then run away!) As the volcano grows, so the GPS system lets scientists measure the change in height.