Surveying
The scale of a tilted photograph of focal length f taken from an altitude H, along the plate parallel through principal point is

f/H
f sec θ/H
f/H cos ½θ
f/H sec θ

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Surveying
Contour interval is

Directly proportional to the flatness of ground
Inversely proportional to the scale of the map
Larger if the time available is more
Larger for accurate works

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