Satellite imagery, like most other types of image or graphical data, are typically obtained in digital format on CD-ROM or, increasingly, via direct download over the Internet. Unlike the graphics that illustrate web pages, however, satellite image files tend to be extremely large in size (300 megabytes is not uncommon, vs. 20 kilobytes for a web graphic) and are usually encoded in a “binary raster” format that can only be manipulated and displayed using software specifically designed for image processing.

When beginning the process we load the image data from the CD-ROM or another location onto the image processing workstation. This image is oriented parallel to the satellite’s orbital path, not “north up,” and is not in any particular map projection