When the first Landsat Earth-observing satellite launched in 1972, virtually every piece of technology that we think of as essential for viewing, sharing, or analyzing digital images — like the internet or DVD's — either hadn’t been invented or commercialized, like the microprocessors that run desktop computers. “It cost about $4,000 for a single Landsat image, and it takes about 9,000 of them to map the land area of the globe,” said Jeff Masek, from NASA. "To make a global image for just one time period would have cost $36 million." But now, in this age where everything is digital and it's easy to exchange information, anyone can download Landsat images for free. Recently, NASA and the U.S. Geological Survey put the finishing touches on a new collection of mapped images covering the entire land surface of the Earth. However, if you want the entire full-size version, it would be as big as the Hoover Dam.
Full article by Nancy Atkinson on Universe Today