Photographic systems are used primarily on airborne platforms. Arial photography is the system most commonly used by cartographers. The high spatial resolution makes it useful in applications such as urban mapping and ground topology. When using arial photographs, the cartographer has to consider scale variations. In an arial photograph, objects at higher altitudes appear larger.
Radial displacement causes objects closest to nadir to have a larger scale.
Nadir is the point directly below the aircraft. The overlap allows photos to be viewed stereoscopically to show relief. The relief view is used to map contours. If scale is not included, the user can often calculate it from objects of known size. Football fields, baseball fields and section lines make good standards for calculating scale.