Possible with a backgroundapp that compares current pos with predfined pos?

Just a hypothetical question.

I am thinking of making an app that read the current GPS position and compares it to several predfined positions. That is not hard but what I need to do is have it run in the background and if the device gets within a certain range of the predfined position it should make the user aware of that prefinded position.开发者_如何转开发

Is this possible? If so can someone give me some suggestions how to think and do this?

---

You can't do it with iPhone SDK 3.0 (as you tagged your message with), but you can with iPhone SDK 4.x There's a section in the multi-tasking docs that talks about doing this, including how to receive location events while in the background.