xRez Extreme Resolution photographs are gigapixel shots of urban and natural environments that allow the viewer to zoom in to ridiculous levels of detail.
Why do we care? No reason, it's just cool. Check out the images of El Capitan and Half Dome in Yosemite. Click on the word "zoom" below the images and you'll be able to drill down from a full view of the monoliths to a level that suddenly makes it interesting to climbers who want to trace a full route up the rock.
Now someone needs to start adding route lines to the pix...