that we want to track an android on a first step, we have the number, and we want to know its location...just to check it if is on a rail station..or on the airport bathroom

LocationManager

public class LocationManager 
extends Object 

java.lang.Object
↳	android.location.LocationManager

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This class provides access to the system location services. These services allow applications to obtain periodic updates of the device's geographical location, or to fire an application-specified Intent when the device enters the proximity of a given geographical location.

You do not instantiate this class directly; instead, retrieve it through Context.getSystemService(Context.LOCATION_SERVICE).

Unless noted, all Location API methods require the ACCESS_COARSE_LOCATION or ACCESS_FINE_LOCATION permissions. If your application only has the coarse permission then it will not have access to the GPS or passive location providers. Other providers will still return location results, but the update rate will be throttled and the exact location will be obfuscated to a coarse level of accuracy.

https://developer.android.com/reference/android/location/LocationManager.html#NETWORK_PROVIDER