You want Google maps to rotate rectangularly when you use your Android device as a GPS in your car. You want to view the map so the width of the screen and height change 90 degrees based on the way you hold the phone (so it responds to gravity). How do you get the screen to adjust to have a layout that is appropriate for holding the smart phone sideways?
Go to the top of the screen and swipe downwards.
Click the "Portrait" icon.
(It should change to auto rotate). That's it.