Ground Truth

Quick Definition From Wikipedia, the free encyclopedia.

"In cartography and analysis of aerial photographs and satellite imagery, the ground truth is the facts that are found when a location is field checked -- that is, when people actually visit the location on foot.

Aerial photographs, satellite images, and maps can be deceiving, while the ground truth is immutable."

For your amusement, here is NASA's "S'COOL" page on Ground Truth.

In practice, children can give us ground truth: