A gas meter to a house can be located on all different sides of the house.
Some gas meters are located in the front of the house, side of the house, back of the house etc.
My gas meter is located at the side of the house and the gas lines leads out to the street but sometimes a gas meter may be located in the back of the house where the gas line leads out to the alley.
I've had a house where the gas meter was located in the back of the house but near the middle of the yard so it may not be right at the back of your house.
If you can't find your gas meter you can have the gas company find and locate it for you and sometimes people have hidden the gas meter underneath something to cover it up.