I’ve learned that, with people who are learning English, it’s best to avoid idioms, slang, figures of speech, etc. What is best is to communicate in simple, concrete terms. If it’s a circle, say “circle” while you are pointing and making a circular motion with your finger. Not only are you giving them directions, you are teaching them a new word.
I had to look, you are right. But the streets themselves are unchanged so from a traffic viewpoint it’s still a square.
Harvard Square is not square. It’s not even round. It’s more a triangle.