This is an example of a car navigation.
Car navigation utilizes GPS to show the travelling direction on the map.
When you turn at an intersection, the map will rotate so that the direction is always
consistent to the where the user is heading.
This is realized by acquiring the position of the car at a regular interval using the GPS
and by estimating the travelling distance and direction from a particular position.
On the other hand, in a portable device for pedestrian navigation, an electronic compass is used
in addtion to the GPS.
What is the reason for this?