I'm making an app that tracks user location. The idea is when a user reaches certain destination, user's iPhone will vibrate and notification will appear on the screen. I also want to keep app running in background when user locks his phone. So the questions are:
You have to implement the Geofencing in your application. You can use raywenderlich demo. Also checkout Apple document for more information.
Application will notify you when you are in region. So you can do whatever you like.