Photogrammetry

Step 1: Understanding the Concept:
Scale in photogrammetry is the ratio of a distance on the photograph (map distance) to the corresponding distance on the ground (ground distance).
Step 2: Key Formula or Approach:
For a truly vertical photograph taken over flat terrain, the scale ( ) is defined as:

Where:
= Focal length of the camera lens.
= Flying height of the aircraft above the Mean Sea Level (MSL).
= Elevation of the ground above the MSL.
Step 3: Detailed Explanation:
If we consider the flying height relative to the ground (let ), the formula simplifies to:

This shows that the scale is directly proportional to the focal length and inversely proportional to the flying height.
A shorter focal length or a higher flying altitude results in a smaller scale (covers more area but with less detail).
Step 4: Final Answer:
The scale of a vertical photograph is the ratio of focal length to flying height.