Aerial photography differs from other types of photography in significant
ways.

Without even getting into the question of atmospheric conditions, and the uses
of infrared imaging materials, we can say that, generally speaking, aerial
photography has a very high information-gathering value. If you're doing
pictorial photography on the ground, you may not need or even want very high
pixel counts, as this only produces gigantic files, that you then have to
reduce to publish on the web, or send as e-mail. In aerial photography though,
even if you're doing oblique, pictorial work, you very often want to crop your
subject to get to the essential matter. Sometimes, in a plane or helicopter,
you cannot get as close as you'd like to your subject, so you end up cropping,
sometimes drastically, which of course digital photos cannot support.

Now, look at technical applications, such as wildlife, geological and
environmental surveys, and it becomes obvious that almost no amount of
information could be "too much". For such uses, film is a great medium,
because it is fast, and very high resolution. The digital vs film "shootouts"
being published today generally concern high-end 6-10MP cameras, compared to
24x36mm film. But most aerial photographers don't use 24x36mm much. The 6x7cm
frames that the ultra-famous Arthus-Bertrand (and, I suspect, the contributor
of these fantastic London shots) uses have 5X the resolution of "standard"
35mm shots. So, something like 30-50MP equivalent. The 5"x5" format of the K20
camera (the Linhof 45EL being the most recent, and most beautiful iteration of
this format) have 17X standard 35mm resolution (100-170MP) and the 9"x9"
format still standard for vertical photogrammetry (used by geological survey
for map-making) is 60X 35mm resolution, which is getting into the GigaPixel
order of magnitude!

As an example of file size, when I take 4X5-inch transparencies or negatives
to the drum scanner, a 20MB file is considered a low-resolution, "dirty" scan,
just to get an idea of what the thing looks like, and is not even scratching
the surface of the information available in the 4X5.

G Faris