This is called endlap . On an air photo, terrain features close to the aircraft appear to move relative to the lower elevation features when the view changes. These displacements can be used to see in 3-D and to measure the elevation of the terrain. Parallax displacements occur parallel to the flight line. Photos taken over areas of varying elevation will exhibit a continuous range of scales.
Maps are orthographic views, photos are perspective views.
The tops of objects in vertical photos are displaced away from their base - this is called relief displacement . Parallax is the difference in the appearance of objects due to a change in perspective. The northern most photo will be placed under the right side of the stereoscope. The stereopair should be moved toward and away from each other until the features overlay one another on the photo pair. C. Place the photo to be annotated to your left with the endlap area to the right, and tape the left edges of the photo.