Final answer:
The pressurization system obtains the landing elevation from the altimeter, which measures atmospheric pressure and converts it into altitude.
Step-by-step explanation:
The pressurization system in an aircraft cabin obtains the landing elevation from the altimeter. The altimeter measures the atmospheric pressure and converts it into a corresponding altitude. During the landing approach, the altimeter provides the current elevation of the aircraft with respect to the ground. This information is used by the pressurization system to adjust the cabin pressure to a suitable level for the passengers.