Play back the last 10,000 years sped up, so that a millenium passes by every minute. For more than seven minutes, the screen displays what looks like a still photograph -- the blue planet Earth, its lands swathed in a mantle of trees. After seven and a half minutes, there's a tiny clearing of forest around Athens. This is the flowering of classical Greece. Little else changes. At nine minutes -- 1,000 years ago -- the forest gets thinner in parts of Europe, Central America, China and India. Twelve seconds from the end, two centuries ago, the thinning spreads a little farther in Europe and China. Six seconds from the end, eastern North America is deforested. This is the Industrial Revolution.

I thought about donating it to a university, but their libraries focus on preservation, they'd have put my collection in a vault and there would have been no access. Along comes the Internet, and I found we could do even more with the digital content than with the originals. We serve over 7000 visitors a day. A typical map library will serve 200 visitors a year.