The photo is taken as a horizontal photo. When the ground is at an average elevation, the ratio of a segment L in the photo to the corresponding horizontal distance L on the ground is ().

Analysis:

Strictly speaking, the photographic scale refers to the ratio of the length of a line in an aerial photograph to the horizontal distance L of the corresponding line on the ground. However, due to the tilt of photographic photos and the ups and downs of terrain, the proportion of photography varies from place to place. We generally refer to the photographic scale, that is, taking photographic photos as horizontal photos and taking the average elevation of the ground. At this time, the ratio of a line segment 1 in the photo to the horizontal distance l of the corresponding line segment on the ground is called the photographic scale 1/m. That is, 1/m=l/L=f/H, where f is the main distance of the photographer and h is the aerial height of the average elevation plane, which is called the aerial height.