Hows does Significant Location Change work?

Can anyone confirm how Significant Location Change works?

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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?

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

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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.