Microsoft's Mark Brown has put up a cool post on his Microsoft Virtual Earth blog. It's part two of a series that's detailing some of the bits and pieces behind the tool that gives you that oh-so-helpful birds-eye view of your dry cleaners.

In this episode Brown sits down with Keystone Aerial Surveys, a Philadelphia-based company that's got less than 50 employees and 14 airplanes doing all the capture work.

Interesting bits:

• Keystone's flights average about 5 hours a trip.
• Each trip brings in about 1,000 super high resolution images which come out to about 100 square miles.
• Certain map suppliers will only shoot during certain parts of the year--Microsoft takes photos year round.
• City images can be some of the toughest shots to get because of shadows.
• Companies like Keystone need to buddy up to air traffic controllers to get special clearance for "loitering" (going back and forth in the same general area).
• Pilots get their flight data from software that maps out areas that need to get captured. You can see a demo of this in action in the first third of the video.
• The "UltraCam" that takes the pictures uses a special infrared sensor that cuts through cloudy spots. You can see it snapping and cutting apart shots once they're up in the air.

The video is a about an hour long, and definitely worth a watch if you like planes and maps. If you're feeling impatient you can skip ahead to the 32:10 mark to get to the good stuff--like when they're flying around to take pictures of your backyard.