It's a problem experienced by viewers on our Facebook page too. You told us that the website often puts you anything between 20 and 187 miles away from their true location.
So why does it happen? Well anything connected to the internet has an IP address which as you might expect allows other computers to work out where it is, at least in cyberspace. Trouble is using an IP address for a physical location may lead you to the sort of problems Facebook is experiencing.
When I post from Facebook at work (in my break obviously) then I'm often tagged in Bloomsbury in London. And by using an online tool like "What is my ipaddress.com" you can see that's where my work computer has it's IP address. Some BBC server in London. Makes sense in cyberspace, produces a bit of a disconnect in the real world.
Facebook told us;
"Facebook's mobile app uses positioning data provided by the phone's operating system. This is compared to a database of place names. Occasionally, inaccurate results will be returned. We are constantly working to refine the technology."
And given our apparent insatiable desire to tell Facebook everything about us sooner or later things will certainly improve. Which of course will allow Facebook to target us with ads even more effectively.
Which just leaves one puzzle. I can understand how an IP address in Birmingham leads to a server in London. What I really don't understand is why Birmingham sometimes becomes Chaddesley Corbett? Is there some massive server farm or internet node I don't know about in the sleep Worcestershire village? If you know more hit me up in the comments.