At the back, what is the correct grammar?

In the front and at the front, do they have the same meaning? what is the correct grammar?

Also sometimes, I have heard people said "in the back", sometimes I have heard "at the back" to tell that the person is at the lawn behind a house. Which one is the correct grammar?
Update: the context.... well suppose you are a property agent. You say, there is a swimming pool at the back of the house? Or At the front lawn, you will see a fountain made of stone.....
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