• In order to prepare the aerial photograph, a flight line is marked on a map called flight map
• These are straight and continuous lines from one end to another and are laid parallel to each other in such way that while the entire is area is covered
• There is 30% overlap in between photographs taken from two consecutive flight lines
• The direction of lines is decided on the basis of requirement of navigation, photo interpretation, shape and size area photographed
• The lateral of side laps depends up on the distance between two consecutive flight lines and as already stated they are arranged to have a side 30% but it should not be less than 15%.

Deviations in Flight line

1. Drift: if is the horizontal displacement of aircraft due to wind from its original determined course or planned flightwhile photographer continues to make exposures oriented to the predetermined flight line.

2. Crab: it is the continuous caused by the failure to orient the camera so that axis perpendicular to the long dimension of the film is parallel to the track of the airplane. This is indicated in vertical photography by sides of photographs not being parallel to the principal point baseline

3. Drift and tilt: should not be exceed 10% of the width, otherwise it may affect in the result in stereoscopic interpretation.

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4. Tilt: is angle between the optical axis of the camera and plumb line for given photograph. Tilt is caused by deviation of the optical axis from the perpendicular. It should not be exceed 2° in normal condition but in extreme it may acceptable up to 5°.

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