Gigapixel images contain about 1 billion pixels. That works out to about 32,768 by 32,768 pixels. The average computer screen is about 1,200 pixels wide so to view a gigapixel image requires you to do a lot of zooming in and out and panning about. A gigapixel image requires lots of memory so viewing an image this large using your average photo software will quickly bring your typical computer to a grinding halt. Special software has been developed to allow you view these high resolution images on a desktop PC. One such program is LizardTech Expressview. You can also view gigapixel images using Google Earth. This Youtube video demonstrates Google Earth’s gigapixel viewing capability.
Xrez is a company that is in the business of creating extremely high-resolution gigapixel photography.