The aerial images of highway section A10 are reductions of the original 1:3000 images taken for PENNDOT on March 28, 2001. The images that PENNDOT is using for the Route 21 project are high-resolution. The scale of 1:3000 means that one inch on the photograph equals 250 feet on the Earth's surface. The images are refered to as "orthographic projections" or "orthos" for short. That means that the raw images were processed so that the projecting lines have been corrected to be perpendicular to the plane of the image. This essentially flattens out the image correcting for camera tilt, terrain relief and Earth's curvature allowing the images to be used for photogrametric or mapping purposes. If you want to know more about the geometry of aerial photography check out the excellent lecture notes from a course at the University of California, Santa Barbara, Georaphy Department.

You can also obtain aerial images from the Microsoft TerraServer website. TerraServer is operated by Microsoft with hardware provided by Compaq and images supplied by the U.S. Geological Survey. You can read more about the technology behind TerraServer. They have 1 meter resolution images of the Masontown area taken on 18 April 1994 and 14 March 1995.