I'd like know what is difference between GPA and core locator in iphone. Also Whether internet needed for GPS?
I think this sentence best sums it up, but I would add the MapKit Framework to the mix
Apple Documentation Location-based information in iOS comprises two pieces: location services and maps. Location services are provided by the Core Location framework, which provides Objective-C interfaces for obtaining information about the user’s location and heading. Maps are provided by the Map Kit framework, which supports both the display and annotation of maps similar to those found in the Maps application.
Internet is not needed for GPS, however, you can improve the location process with an internet connection or an mobile network.
The first technique would be triangulation from the next cell towers where the phone is booked into, the other technique is loading the almanach used to translate the time send out by the sattelites into a position. This is a ~500b file which is send every 20 minutes so you can speed up the first position fix by up to 20 minutes when the almanach is loaded from somewhere else. However, the almanach is usually cached and can be used around one week before there is a need for a new one.