You know ... I’m typing this on an iPad, which has the same operating system as the iPhone. One of the nice things about this iPad, is that I can take pictures and know where they’ve been taken. It also shows the direction I was shooting, along with all the other information.
Now, sometimes, the EXIF information is wrong in regards to the coordinates (slightly off) and I don’t know why it does that, but a few show up that way. So I went looming for something to change the information so I could put it back in the correct location. Anyway, the point is - I can change that information and show a different location than was originally recorded. This can be done. I’ve actually done it on mine.
On an iPhone the GPS is not GPS. It’s triangulation between cell towers or wifi.
So, if you don’t have access to more than one source, it will approximate.
It’s not accurate at all, relatively speaking.
I can fill you in on why the coordinates are off slightly.
My small hand held GPS locator is always a few hundred yards off from the data on my high precision surveying receivers, even before processing the data. It takes a long time for the hand held units to achieve an accurate position.
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You can add to the exif data, but you cannot actually change it. You can also delete it completely.