![]() ![]() Īs commercial off-the-shelf GIS software, GIS installations, and GIS data proliferated in the 1980s, scholars began to look for conceptual models of geographic phenomena that seemed to underlay the common data models, trying to discover why the raster and vector data models seemed to make common sense, and how they measured and represented the real world. This led to efforts at the Harvard Lab and elsewhere focused on developing a new generation of generic data models, such as the POLYVRT topological vector model that would form the basis for commercial software and data such as the Esri Coverage. During the 1970s, the early systems had produced sufficient results to compare them and evaluate the effectiveness of their underlying data models. Most first-generation GIS were custom-built for specific needs, with data models designed to be stored and processed most efficiently using the technology limitations of the day (especially punched cards and limited mainframe processing time). ![]() Unlike CGIS, these were all raster systems inspired by SYMAP, although the MLMIS was based on subsections of the Public Land Survey System, which is not a perfect regular grid. ![]() Like the CGIS, early GIS installations in the United States were often focused on inventories of land use and natural resources, including the Minnesota Land Management Information System (MLMIS, 1969), the Land Use and Natural Resources Inventory of New York (LUNR, 1970), and the Oak Ridge Regional Modelling Information System (ORRMIS, 1973).Dual Independent Map Encoding (DIME, US Census Bureau, 1967) was perhaps the first robust vector data model incorporating network and polygon topology and attributes sufficient to allow address geocoding.The Canadian Geographic Information System (by Roger Tomlinson, Canada Land Inventory, developed 1963–1968) stored natural resource data as "faces" (vector polygons), although these were typically derived from raster scans of paper maps.The GRID package, developed at the lab in 1969 by David Sinton, was based on SYMAP but was more focused on the permanent storage and analysis of gridded data, thus becoming perhaps the first general purpose raster GIS software. SYMAP (by Howard Fisher, Harvard Laboratory for Computer Graphics and Spatial Analysis, developed 1963–1967) produced raster maps, although data was usually entered as vector-like region outlines or sample points then interpolated into a raster structure for output.The first true GIS software modeled spatial information using data models that would come to be known as raster or vector: The earliest computer systems that represented geographic phenomena were quantitative analysis models developed during the quantitative revolution in geography in the 1950s and 1960s these could not be called a geographic information system because they did not attempt to store geographic data in a consistent permanent structure, but were usually statistical or mathematical models. While the unique nature of spatial information has led to its own set of model structures, much of the process of data modeling is similar to the rest of information technology, including the progression from conceptual models to logical models to physical models, and the difference between generic models and application-specific designs. Data models are implemented throughout the GIS ecosystem, including the software tools for data management and spatial analysis, data stored in a variety of GIS file formats, specifications and standards, and specific designs for GIS installations. For example, the vector data model represents geography as collections of points, lines, and polygons, and the raster data model represent geography as cell matrices that store numeric values. Generally, such data models represent various aspects of these phenomena by means of geographic data, including spatial locations, attributes, change over time, and identity. For broader coverage of this topic, see Data model.Ī geographic data model, geospatial data model, or simply data model in the context of geographic information systems, is a mathematical and digital structure for representing phenomena over the Earth.
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