http://info.r.usgs.gov/fact-sheets/glis/GLIS.html
The Global Land Information System (GLIS) is an interactive computer system developed by the US Geological Survey (USGS) for scientists seeking sources of information about the Earth's Land surfaces. GLIS contains metadata or descriptive information about data sets. It includes references to regional, continental, and global land information including land use, land cover, and soils dat, cultural and topographic data, and remotely-sensed satellite and aircraft data. GLIS graphic services are also available.