For additional reading, take a look at this website on aerial photography and remote sensing . Also take a look at the Slagboom en Peeters photo galleria from the Netherlands. Remotely sensed imagery is the basis for most mapping projects of the earth's surface.
Imagery is relatively easy to acquire, inexpensive per ground unit coverage, and timely.
Both aerial photography and electronic imagery are extremely useful for detecting landscape patterns . Much of the U.S. has been photographed since the 1930s and provides a continual record of landscape change. Image maps are used by planners, ecologists, earth scientists, engineers, and the military. Bear in mind, however, that image maps usually do not have a legend that explains the features thereon. Therefore, one must learn image interpretation skills to effectively use these sources of data.