How does Google Play determine the region on a tablet without SIM card I know Google Play uses SIM card to determine the region on cell phones. And I know Market Unlocker and Market Enabler.

How does Google Play determine your region on a tablet without SIM card?

And how to change it? I have access to IP address where Google Play is available. And I own a credit card whose billing address is in a country where Google Play paid apps are available.
Google uses your IP Address and visible WiFi networks, as well as the information from the Google Account you used to determine your region.