Hows does Significant Location Change work?

Can anyone confirm how Significant Location Change works?

1. movement is calculated when the iPhones cell receiver swaps from one cell tower to another as the user moves around?

2. movement is calculated by triangulating b开发者_Go百科etween "visible" cell towers to best calculate the users position?

3. movement is calculated by triangulation between "visible" cell towers based on the settings associated with desiredAccuracy?

Number 1 is the right answer. This is the reason, those updates come not very often.

Don't rely on it working in a specific way. If the way it works isn't documented, you should be open to changes in that respect.