Which method permits drawing contour lines and other detail by using two overlapping air photos under a stereoscopic instrument?

• A. Stereoscopic vision
• B. Scribing
• C. Squeeze
• D. Symbols

Answer: (A)

Stereo vision lets you extract height information from two overlapping air photos viewed together in a stereoscope. When the pair is fused in 3D, the slight parallax between corresponding points reveals how high or low features stand relative to one another. By tracing contours at a chosen elevation interval while interpreting that relief in the stereo image, you can produce detailed topographic lines and other features. This stereo interpretation is the fundamental photogrammetric method for deriving contour and terrain detail from aerial imagery. The other approaches aren’t about using stereo parallax to recover elevation—scribing is manual drawing, squeezing is related to film handling, and symbols refer to map notation after the data is produced.