Aerial imagery is the technique of photographing a land area from a high altitude, usually from an airplane. This can also be done from spacecraft, in which case, it is called satellite imagery. Aerial imagery, along with satellite imagery, plays and important role in cartography.
Digital aerial imagery is widely used today as a source to collect a wide variety of information, including the location of transportation routes, steams, and lakes, to the outlines of buildings and farm fields. Digital images, for example, are displayed in 9-1-1 response centers to pinpoint the location of emergency callers that use mobile phones and in police cars and fire trucks to analyze emergency situations.
Although both maps and aerial photos present a "bird's-eye" view of the earth, aerial photographs are NOT maps since they display a high degree of radial distortion and do not maintain a constant scale across the image. However, orthophotographs are aerial photographs that have been corrected, becoming a map allowing accurate spatial measurements.
For finding aerial imagery, visit our catalog of aerial photgraphy or our online resource listing.
Season & film type
It's important to know the month or season of the photography for determining whether the photography is "leaf-on" (deciduous vegetation with leaves) or "leaf-off". To acquire leaf off photography, the window of opportunity to fly and capture the photography is rather small which usually happens in early Spring before the leaves come out.
Typically black-and-white film costs less than color film. Depending on the area of coverage, this can be a costly factor to consider. Listed are types of film used for photography:
- B&W = Back-and-White (panchromatic)
- B&W IR = Black-and-White Infrared*
- COLOR = Natural Color
- COLOR IR = Color Infrared (false color)
*Infrared film is typically used to view differences between types of vegetation and to clearly see the distinction between water and land.
Scales
Most aerial photography is taken with a large format camera using 9" x 9" film. Since the size of aerial film is the same, the scale and thus the detail visible on a photo depends on flying height above the ground. As an example, a photo at 1:20,000 scale (1" = 1667') covers one quarter the area and shows objects at twice the size as a 1:40,000 scale (1" = 3,333') photo. This results because the 1:20,000 scale photo was flown at half the altitude of the 1:40,000 scale photo.
When enlargements of the photos are produced, scale increases.
Large scale:
A large scale photo (eg., 1:2,500) means that ground features are at a larger, more detailed size. The area of ground coverage depicted on a large-scale photo is less than at a similar scale.Small scale:
A small-scale photo (eg., 1:60,000) means that ground features are at a smaller, less detailed size. The area of ground coverage that is depicted on a small-scale photo is more than at a larger-scale.
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