What tool is used to determine the size of objects in an aerial photograph?

The scale bar is a critical tool when it comes to determining the size of objects in an aerial photograph. It provides a visual representation of the scale of the map or photograph, indicating the relationship between distance on the image and actual ground distances. This allows users to measure the size of features by comparing them to the scale bar.

For instance, if the scale bar illustrates that one inch on the photograph equates to 100 feet on the ground, one can accurately estimate the real-world dimensions of objects seen in the photograph by measuring their size in inches or centimeters on the image and converting that measurement using the scale provided.

The other tools mentioned serve different purposes. The legend explains the symbols used on the map, the grid system provides a reference framework for locating features, and the north arrow indicates orientation. While all of these elements are important for understanding and navigating maps and photographs, the scale bar is specifically designed to provide size and distance information.