Aerial photography is the art of taking photos of the ground while not standing on a ground structure with cameras mounted on aircrafts, balloons, helicopters, dirigibles or rockets. The first person who practiced aerial photography was Nadar, a French balloonist who made the first pictures over Paris in 1858 and thus remained in the history of photography.
Aerial photography was used by the army for the first time in World War I, it is also applied in field studies like cartography, archeology, landing use plans, military or economical espionage, advertising and, last but not least in cinematography. In the last decades environmental programs used aerial photography to support their ecological demands.
Many companies who are trying to map the city turn to small radio controlled aircrafts especially designed for taking photos. They use this solution because flight over residential neighborhoods is restricted at a certain height. On the other hand, American laws allow taking aerial pictures over private zones, because anything capable of being seen from space is not considered private.
Many amateurs that can't afford renting a plane or having a pilot license can buy an astro-cam or some oracle rocket as a solution to continue being interested in aerial photography as a hobby. Aerial photography has many challenges that are not applicable in classical photography.
One of the problems with aerial photography is the perspective correction. Air pictures are made under a certain angle of the photographed object; this may result in an incorrect perspective where near objects look too large if compared to far away targets. So a perspective correction is needed to ensure the best of outcomes.
Aerial photography is mapped with real world targets like buildings, a process known as registration. As an example, think of a road photography seen from above, it can be simply converted to a line. Another problem is that when you want to photograph an entire city for instance.
Of course you can go to higher altitudes and take the whole picture but what if you need it at a higher resolution? The stitching technique is required here as it implies making as many photos as needed and then joining them together. This process as simple as it might seem takes hours of preparation for good results.
Aerial photography plays an important role in the evaluation of buildings or large properties and the best pictures in this case are made from the helicopter. It's far easier to photograph a mall from a helicopter than from a plane, the explanation is that a plane simply can't stay still in the same place, while a helicopter can. However, when you try to sell a larger estate use an airplane for a faster evaluation and the best of results.