This map shows light sources from human settlements around the world observed during 1999. The Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) has a unique low-light imaging capability. developed for the detection of clouds using moonlight. In addition to moonlit clouds, the OLS also detects lights from human settlements, fires, gas flares, heavily lit fishing boats, lightning and the aurora. By analyzing the location, frequency, and appearance of lights observed in an image times series, it is possible to distinguish four primary types of lights present at the earth's surface: human settlements, fires, gas flares, and fishing boats. This layer is part of the Nighttime Lights of the World dataset, a satellite-based global inventory of human settlements, derived from nighttime data from the DMSP. This dataset is intended for researchers, students, and policy makers, and the general public for reference and mapping purposes, and may be used for basic applications such as viewing, querying, and map output production, or to provide a basemap to support graphical overlays and analysis with other spatial data. National Geophysical and Solar-Terrestrial Data Center. (2003). Nighttime Lights of the World - Human Settlements, 1999. National Geophysical and Solar-Terrestrial Data Center. Available at: http://purl.stanford.edu/gb553qr3585. This layer is presented in the WGS84 coordinate system for web display purposes. Downloadable data are provided in native coordinate system or projection.