To appear skilled in the art can be defined both saying the digital electronics uses discrete values ​​with magnitudes, while the electronic analog magnitudes used with continuous values​​. 

To understand we can also say that a Digital Inputs states we measured 1/0, ON / OFF, ON / OFF, while an Analog inputs can measure broader values ​​such as voltage 3-5 volts with all intermediate values. 

With this earthly definition be easy to realize that I know a digital input via GPS device if the engine is running, if a door is open or closed or if the alarm has been triggered by robbery in their service routes or deliveries tasks. 

Basically, the GPS Trackers offer us 1 or more entries which connect the positive cable that will power when one of the two two events (on / off) occurs. 

This is the conceptual starting point. As the GPS Tracker is more complete we will find more Digital Inputs, variable states of on / off with positive or negative charge and are more able to withstand more voltage or amperage for each entry and also for control more event management.