Final answer:
The center of an aerial photo is referred to as its principal point which is directly beneath the camera's lens and serves as a pivotal reference for accurately mapping ground features.
Step-by-step explanation:
When looking down on an aerial photo, the center of the photo is referred to as its principal point. This point is crucial in the interpretation and analysis of aerial photographs because it is the point directly beneath the camera's lens at the time of exposure and is considered the photo's geometric center. Geographers and mapmakers use the principal point as a reference for measuring and orienting images in their proper geographic space. Understanding the principal point helps in accurately mapping features from the aerial photograph onto a coordinate system on the ground.