This datalayer is a point shapefile that shows long-term (1931-1960) mean monthly values for cloud cover on a global terrestrial grid at 0.5 degree longitude/latitude spatial resolution. The dataset is a derived portion of the Global Climate Database (May 15, 1996) which is an updated version of the IIASA database for mean monthly values of temperature, precipitation and cloudiness on a global terrestrial grid (1991), first produced by Rik Leemans and Wolfgang Cramer, and published by the International Institute of Applied Systems Analyses and also distributed by the National Institute of Public Health and Environmental Protection (Netherlands). This version of the datalayer appears as part of the USGS Global GIS : global coverage database (2003). Cloud Coverage or Cloudiness is defined as the actual number of bright sunshine hours over the potential number, and is thus expressed as a percentage figure. A high percentage means more sunshine and fewer clouds. The USGS Global GIS database contains a wealth of USGS and other public domain data, including global coverages of elevation, landcover, seismicity, and resources of minerals and energy at a nominal scale of 1:1 million. The U.S. Geological Survey (USGS) and The American Geological Institute (AGI) announced a cooperative agreement that will focus on making the USGS Global Geographic Information System (GIS) database readily available to educators and the general public in the form of a DVD based world atlas.