The majority of USGS aircraft photography is used for cartographic purposes. Image distortion is minimized when photographs are acquired looking straight down or vertically. Scale refers to the relationship of distance on photographs or maps to the actual ground distance. It is a ratio that could represent any unit of measurement. Resolution refers to the ability to distinguish the smallest visible objects on a photograph.
Resolution is a result of the combination of film type and the camera lens system.
A flight line is a path on a map or chart to represent the track over which an aircraft has been flown or is to fly. Focal length is the distance measured from camera lens to film. This depends on the purpose for which the photograph is to be used. For land cover mapping, most people prefer CIR . If the photograph is a gift or is to be used as a wall hanging, film type may not be as serious a consideration.