(1) The ratio of a distance on an image or map to its corresponding distance on the ground. The scale of an image varies from point to point because of tilt and relief, but is usually taken as f/H where f is the principal distance (focal length) of the sensor, and where H is the height of the sensor above mean ground elevation. Scale may be expressed as a ratio, e.g. 1:24,000; a representative fraction, e.g. 1/24,000; or an equivalence, e.g. 1 in = 2,000 ft.