Why can photogrammetry survey topographic maps?

Because photogrammetry can convert aerial photos obtained by the ground according to the central projection law into orthographic projection maps expressed by drawing scale.

Photogrammetry is to measure and judge the size, shape and spatial position of objects on the ground according to the ground photos taken by aircraft, so as to establish topographic map information data of the shooting area. Aerial photography is to use the camera installed in the lower part of the plane to fly at a certain height and take continuous overlapping photography of the area to be mapped at a specified time interval. It is required that the pictures taken can cover the whole area to be measured and overlap to some extent. Generally speaking, the heading overlap should reach 60% ~ 70%, and the lateral overlap should reach 15% ~ 30%.