Airspace is divided up by region and altitude. Wherever you are, there is a controller responsible for you. He has the plane on radar and gives you instructions to keep you separated from other planes. The airspace isn’t just an empty system, it has agreed upon fixed points between which you navigate. You will get instructions like “head to XYZ and hold” to get you out of a possible conflict (“hold” meaning that you loop around that fixed point). Or the controller puts you on a different altitude to avoid conflict.
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