Photo scale. Scale is a ratio of distances:

S = distance on photograph / distance on the ground

For an aerial photograph, this works out to:

S = f / H

• f — camera focal length.
• H — flying height above the terrain.

Scale can be expressed three ways: - Verbal — “1 cm equals 1 km”. - Representative fraction / ratio — 1/100 000 or 1:100 000. - Graphic (bar) scale — a labeled bar on the map.

• Rule: larger RF denominator → smaller scale (a 1:100 000 photo is smaller scale than 1:10 000).