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GIS is an acronym for Geographic Information System. It refers to a computer system that can work with geographic information in a number of ways, initially by capturing it, and then by storing it in order to analyze it and display it in various ways. Any location-related data and some data that is not location-related can be collected, stored, analyzed, and presented through such a system. Any time that GIS data is converted to a mapped format — which is often, because maps are a standard and useful way to convey location-based data — GIS mapping is taking place. Other types of data reports from GIS data include charts and graphs, and GIS mapping can be used for a variety of purposes, including mapmaking, tracking migration routes, land planning and site selection, weather forecasting, emergency response planning, analyzing patterns of disease spread or environmental damage, analysis of sales, and to map patterns of discrimination.
Data for GIS mapping may be collected and entered into a GIS system in a variety of ways. GPS (Global Positioning System) receivers can be used to directly upload data collected in the field. Existing paper maps can sometimes be scanned into the system or traced by hand — though some may have to be redrawn — while at the other extreme of technology, satellite images, as well as aerial photography, are also used for data collection. Tabular information and other types of data sets, possibly collected for other purposes, can also be included in the compilation of data.
GIS mapping can either generate an original map or create an overlay for an existing map. There are a number of formats available for GIS mapping, some of which are unique to the United States Geological Survey (USGS). The Digital Line Graph (DLG) shows cartographic information through a digital vector representation. Digital Elevation Model (DEM) — also known as a Digital Terrain Model (DTM) — uses a digital raster form instead, as does Digital Raster Graphic (DRG). A Digital Orthophoto Quadrangle (DOQ) is a computer version of an aerial photograph corrected for camera tile and terrain relief and combined with map qualities, and Digital Surface Model (DSM) may also be used.
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