I am not sure if I used the right forum to ask this question. If it is wrong, please point me the right one.
I understand in general how A-GPS works with cell towers, and how it depends on the data signal. But there are some thing I don't understand fully yet.
I have one phone primarily used in cities, and it is equipped with A-GPS only. My service provider has certain coverage. But even I drive outside my service provider's coverage I am still able to navigate with offline map.
I have another phone equipped with A-GPS only, I used it to travel in other countries thus I don't even bother to insert a SIM card or use roaming service. Basically it is a just a mini tablet. But in cities I was still able to find myself on offline maps, see myself moving on the maps and so on. In one case I was deep is the Amazon rain forest I had no way to locate myself.
So my questions is if A-GPS depends on cell towers to obtain the locations, does it mean as long as there are towers around, it does not matter I can have service with them or not, then I can use A-GPS?