How does external GPS device work with iPhone and iPad?

It seems iPhone (and iPad) actually has a standard feature that is called external GPS device?

I hope to find out more about it:

1. First of all, why would we use an external GPS device? I can understand if it is wireless-only iPad, then it has no GPS hardware and it is "best guessed by wireless", so an external GPS device can help, but what about for iPhone -- why do we need it?

2. If it is external GPS device, is it by BlueTooth only? Can it be by WiFi, or by lightning connector, USB-C if it is iPad Pro, or possibly, another other method? (such as using the Internet to pass the location to iPhone, instead of BlueTooth?)

3. Does it in general work for iPhone and iPad both?

4. So the device can also move around from the true GPS location, such as for whatever reason, simulate a location that is 20 feet away? Or even to 50 miles away? What are some examples of such devices?

The question is to understand about "external GPS devices", which I never knew is actually a standard feature for the iPhone / iPad.

Per specs, only iPads with cellular modems have GPS hardware built in—where by definition all iPhones will have it.

There's a discussion thread in Apple communities that appears well-sourced with a few links to more information.

Speaking from experience, full-fledged GPS in an iOS device WILL drain battery quite quickly—due to the need for satellite tracking. That can be an unwelcome surprise in the wilderness—and something dedicated GPS devices may be better suited for.

Another example is aviation-use iPads in the cockpit for management/flight planning, where external GPS devices run the risk of interfering with the aircraft's installed GPS transceivers.